Date:   Thu, 28 Jul 2022 17:47:57 +0200
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Edward-JW Yang <edward-jw.yang@...iatek.com>
Cc:     Johnson Wang (王聖鑫) 
        <Johnson.Wang@...iatek.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "krzysztof.kozlowski+dt@...aro.org" 
        <krzysztof.kozlowski+dt@...aro.org>,
        "mturquette@...libre.com" <mturquette@...libre.com>,
        "sboyd@...nel.org" <sboyd@...nel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-clk@...r.kernel.org" <linux-clk@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        Project_Global_Chrome_Upstream_Group 
        <Project_Global_Chrome_Upstream_Group@...iatek.com>,
        Yu-Chang Wang (王煜樟) 
        <Yu-Chang.Wang@...iatek.com>,
        Kuan-Hsin Lee (李冠新) 
        <Kuan-Hsin.Lee@...iatek.com>, Chen-Yu Tsai <wenst@...omium.org>
Subject: Re: [RFC PATCH 2/2] clk: mediatek: Add frequency hopping support

Il 28/07/22 17:30, Edward-JW Yang ha scritto:
> Hi AngeloGioacchino,
> 
> Thanks for the discussion.
> 
> On Thu, 2022-07-28 at 16:21 +0800, AngeloGioacchino Del Regno wrote:
>> Il 28/07/22 06:37, Edward-JW Yang ha scritto:
>>> Hi AngeloGioacchino,
>>>
>>> Thanks for the advices.
>>>
>>> On Thu, 2022-07-21 at 17:43 +0800, AngeloGioacchino Del Regno wrote:
>>>> Il 20/07/22 15:51, Edward-JW Yang ha scritto:
>>>>> Hi AngeloGioacchino,
>>>>>
>>>>> Thanks for all the advices and examples.
>>>>>
>>>>> On Thu, 2022-07-14 at 19:04 +0800, AngeloGioacchino Del Regno wrote:
>>>>>> Il 06/07/22 15:07, Edward-JW Yang ha scritto:
>>>>>>> On Wed, 2022-06-29 at 16:54 +0800, Chen-Yu Tsai wrote:
>>>>>>>> On Tue, Jun 28, 2022 at 6:09 PM AngeloGioacchino Del Regno
>>>>>>>> <angelogioacchino.delregno@...labora.com> wrote:
>>>>>>>>>
>>>>>>>>> Il 24/06/22 09:12, Edward-JW Yang ha scritto:
>>>>>>>>>> Hi AngeloGioacchino,
>>>>>>>>>>
>>>>>>>>>> Thanks for all the advices.
>>>>>>>>>>
>>>>>>>>>> On Mon, 2022-06-13 at 17:43 +0800, AngeloGioacchino Del Regno wrote:
>>>>>>>>>>> Il 12/06/22 15:54, Johnson Wang ha scritto:
>>>>>>>>>>>> Add frequency hopping support and spread spectrum clocking
>>>>>>>>>>>> control for MT8186.
>>>>>>>>>>>>
>>>>>>>>>>>> Signed-off-by: Edward-JW Yang <edward-jw.yang@...iatek.com>
>>>>>>>>>>>> Signed-off-by: Johnson Wang <johnson.wang@...iatek.com>
>>>>>>>>>>>
>>>>>>>>>>> Before going on with the review, there's one important consideration:
>>>>>>>>>>> the Frequency Hopping control is related to PLLs only (so, no other clock
>>>>>>>>>>> types get in the mix).
>>>>>>>>>>>
>>>>>>>>>>> Checking the code, the *main* thing that we do here is initializing the
>>>>>>>>>>> FHCTL by setting some registers, and we're performing the actual frequency
>>>>>>>>>>> hopping operation in clk-pll, which is right but, at this point, I think
>>>>>>>>>>> that the best way to proceed is to add the "FHCTL superpowers" to clk-pll
>>>>>>>>>>> itself, instead of adding multiple new files and devicetree bindings that
>>>>>>>>>>> are specific to the FHCTL itself.
>>>>>>>>>>>
>>>>>>>>>>> This would mean that the `fh-id` and `perms` params that you're setting in
>>>>>>>>>>> the devicetree get transferred to clk-mt8186 (and hardcoded there), as to
>>>>>>>>>>> extend the PLL declarations to include these two: that will also simplify
>>>>>>>>>>> the driver so that you won't have to match names here and there.
>>>>>>>>>>>
>>>>>>>>>>> Just an example:
>>>>>>>>>>>
>>>>>>>>>>>          PLL(CLK_APMIXED_CCIPLL, "ccipll", 0x0224, 0x0230, 0,
>>>>>>>>>>>
>>>>>>>>>>>              PLL_AO, 0, 22, 0x0228, 24, 0, 0, 0, 0x0228, 2, FHCTL_PERM_DBG_DUMP),
>>>>>>>>>>>
>>>>>>>>>>> Besides, there are another couple of reasons why you should do that instead,
>>>>>>>>>>> of which:
>>>>>>>>>>>        - The devicetree should be "generic enough", we shall not see the direct value
>>>>>>>>>>>          to write to the registers in there (yet, perms assigns exactly that)
>>>>>>>>>>>        - These values won't change on a per-device basis, I believe? They're SoC-related,
>>>>>>>>>>>          not board-related, right?
>>>>>>>>>>>
>>>>>>>>>>> In case they're board related (and/or related to TZ permissions), we can always add
>>>>>>>>>>> a bool property to the apmixedsys to advertise that board X needs to use an
>>>>>>>>>>> alternative permission (ex.: `mediatek,secure-fhctl`).
>>>>>>>>>>
>>>>>>>>>> I think we should remain clk-fhctl files because FHCTL is a independent HW and is
>>>>>>>>>> not a necessary component of clk-pll.
>>>>>>>>>
>>>>>>>>> I know what FHCTL is, but thank you anyway for the explanation, that's appreciated.
>>>>>>>>> In any case, this not being a *mandatory* component doesn't mean that when it is
>>>>>>>>> enabled it's not changing the way we manage the PLLs..........
>>>>>>>>>
>>>>>>>>>> Frequency hopping function from FHCTL is not used to replace original flow of
>>>>>>>>>> set_rate in clk-pll. They are two different ways to change PLL's frequency. The
>>>>>>>>>
>>>>>>>>> I disagree: when we want to use FHCTL, we effectively hand-over PLL control from
>>>>>>>>> APMIXEDSYS to the Frequency Hopping controller - and we're effectively replacing
>>>>>>>>> the set_rate() logic of clk-pll.
>>>>>>>
>>>>>>> Do you mean we need to drop the current set_rate() logic (direct register write) and
>>>>>>> use Frequency Hopping Controller instead?
>>>>>>>
>>>>>>
>>>>>> On PLLs that are supported by the Frequency Hopping controller, yes: we should
>>>>>> simply use a different .set_rate() callback in clk-pll.c, and we should return
>>>>>> a failure if the FHCTL fails to set the rate - so we should *not* fall back to
>>>>>> direct register writes, as on some platforms and in some conditions, using
>>>>>> direct register writes (which means that we skip FHCTL), may lead to unstable
>>>>>> system.
>>>>>>
>>>>>> This means that we need logic such that, in mtk_clk_register_pll(), we end up
>>>>>> having something like that:
>>>>>>
>>>>>> if (fhctl_is_enabled(pll))
>>>>>> 	init.ops = &mtk_pll_fhctl_ops;
>>>>>> else
>>>>>> 	init.ops = &mtk_pll_ops;
>>>>>>
>>>>>>> I need to mention that not all PLL support FHCTL, only those PLLs with FHCTL HW can
>>>>>>> choose to use FHCTL. Take 8186 for example, there are three PLLs don't support FHCTL
>>>>>>> HW.
>>>>>>
>>>>>> Where we declare the PLLs, for example, in clk-mt8186-apmixedsys.c, we can declare
>>>>>> that such PLL can be managed by FHCTL, for example:
>>>>>>
>>>>>> 	PLL(CLK_APMIXED_ARMPLL_LL, "armpll_ll", 0x0204, 0x0210, 0,
>>>>>>
>>>>>> 	    PLL_AO, 0, 22, 0x0208, 24, 0, 0, 0, 0x0208),
>>>>>>
>>>>>> becomes
>>>>>>
>>>>>> 	PLL(CLK_APMIXED_ARMPLL_LL, "armpll_ll", 0x0204, 0x0210, 0,
>>>>>>
>>>>>> 	    PLL_AO, 0, 22, 0x0208, 24, 0, 0, 0, 0x0208, true);
>>>>>>
>>>>>> where 'true' means "FHCTL is supported".
>>>>>
>>>>> Does it still have an independent FHCTL driver after modifying to this? From your example,
>>>>> setup a clk_ops and add FHCTL properities into PLL(), seems FHCTL driver is merged into
>>>>> clk-pll and become part of clk-pll driver.
>>>>>
>>>>
>>>> The direct-MMIO part of FHCTL becomes part of the clk-pll driver, yes - but then
>>>> I also find it unacceptable to embed the IPI communication inside of there, so we
>>>> can have an "external" helper for that.
>>>
>>> I think clk-pll driver should focus on PLL HW itself. Since PLL can work alone without
>>> FHCTL, adding FHCTL control into clk-pll may be a little strange. For this PLL+FHCTL
>>> combination, I want to add a new type of clock driver, like clk-pll-fh. It might be a
>>> easier way to maintain FHCTL HW related changes and won't affect to clk-pll.
>>>
>>
>> That makes sense, and it's doable as long as we're not duplicating clk-pll's code
>> to clk-pll-fh and also as long as we're hardcoding the availability of FHCTL in the
>> SoC-specific clock drivers like I explained in the PLL macro from the previous
>> example. Let's go!
>>
>>
>>>>
>>>>
>>>>> We tend to have an indepentent driver and dts for FHCTL, and mutate only .set_rate()
>>>>> callback function instead of whole clk_ops. The boot-up sequence is like:
>>>>>
>>>>> 1. clk-pll + clk dts
>>>>> 	probe  -> clk-pll original flow, nothing to change
>>>>>
>>>>>            /* clk-pll provide multation API for set_rate */
>>>>> 	/* mutate necessary set_rate() instead of mutating all ops */
>>>>> 		def register_fhctl_set_rate(pll_name, callback)
>>>>> 			ops = find_pll_ops_by_name(pll_name)
>>>>> 			log("change set_rate to fhctl callback for $pll_name")
>>>>> 			ops->set_rate = callback
>>>>>
>>>>> 2. FHCTL driver + fhctl dts
>>>>> 	probe
>>>>> 		options = parsing dts (board specific, hopping disalbe or ssc-rate)
>>>>> 		init FHCTL HW
>>>>> 		for PLL in dts
>>>>> 			if (ssc-rate > 0)
>>>>> 				enable_ssc(ssc-rate)
>>>>> 			if (hop-enabled)
>>>>> 				/* mutate CCF set_rate, FHCTL engaged CCF */
>>>>> 				register_fhctl_CCF(pll_name, callback)
>>>>>
>>>>
>>>> I really don't like having PLL names in devicetree: they're already defined in
>>>> clock drivers and they will change on a per-SoC basis - and we do have per-SoC
>>>> drivers...
>>>>
>>>> Whatever goes to devicetree should be something that we need to vary on a
>>>> per-board/platform(project) basis, so, enablement of FHCTL per-pll (by using
>>>> handles and numeral bindings as per the example that I previously wrote),
>>>> enablement of spread spectrum and its rate... and nothing else.
>>>
>>> OK, we will remove PLL names in devicetree.
>>>
>>
>> Great.
>>
>>>>
>>>>>>
>>>>>> Then, we register the PLLs with something like:
>>>>>>
>>>>>> mtk_clk_register_plls(node, plls, num_plls, clk_data, fhctl_register_version);
>>>>>>
>>>>>> ...where fhctl_register_version is used to assign the right fhctl register offsets.
>>>>>> Also, it's not needed to assign all of the register offsets statically, because
>>>>>> they can be easily calculated based on the number of supported PLLs, since the
>>>>>> registers are structured like
>>>>>>
>>>>>> [FHCTL GLOBAL REGISTERS] <--- hp_en...slope1
>>>>>> [FHCTL SSC GLOBAL REGISTERS] <--- DSSC_CFG, DSSC0...x_CON
>>>>>>
>>>>>> [FHCTL PER-PLL REGISTERS] <--- CFG...MON
>>>>>> ^^^ where this is repeated X times for X PLLs.
>>>>>>
>>>>>> so, keeping the example of MT8186, we can get the per-pll register like:
>>>>>>
>>>>>> #define FHCTL_PLL_OFFSET	0x3c
>>>>>> #define FHCTL_PLL_LEN		0x14
>>>>>>
>>>>>> #define FHCTLx_CFG(pll_id)	(FHCTL_PLL_OFFSET + (pll_id * FHCTL_PLL_LEN))
>>>>>> #define FHCTLx_UPDNLMT(pll_id)	(FHCTL_PLL_OFFSET + (pll_id * FHCTL_PLL_LEN) + 0x4)
>>>>>> #define FHCTLx_DDS(pll_id)	(FHCTL_PLL_OFFSET + (pll_id * FHCTL_PLL_LEN) + 0x8)
>>>>>>
>>>>>> we don't need to put all of them in a structure and for each PLL.
>>>>>
>>>>> We use structure instead of using macros is because the register offset may have
>>>>> difference between ICs. If we use macro, we need to maintain different versions of macros.
>>>>> Using structure to store these register offsets is more flexible.
>>>>>
>>>>
>>>> I understand. What I don't like about your specific approach is the amount of
>>>> register offsets that we store in that structure, looks like it's a bit too many.
>>>>
>>>> I've seen that there's a common pattern at least by checking downstream 5.10 and
>>>> MT8186/95 layouts, so I still think that using these macros will be beneficial.
>>>>
>>>> We can always add parameters to the structure in a later commit: in my opinion,
>>>> that will help to engineer a better, shorter, cleaner solution for calculating
>>>> these registers anyway... but I will leave this choice to you, anyway, since you
>>>> know about way more SoCs than I do.
>>>
>>> OK, we will reduce the structure.
>>>
>>
>> Perfect!
>>
>>>>
>>>>>>
>>>>>>> So, we need both APMIXEDSYS and Frequency Hopping Controller in set_rate() logic to
>>>>>>> handle this two types of PLL.
>>>>>>>
>>>>>>
>>>>>> As already said, we preventively know which PLLs support FHCTL and which does not,
>>>>>> so we can use a different .set_rate() callback.
>>>>>
>>>>> Ok, we can use a different .set_rate() callback when fhctl driver probing.
>>>>>
>>>>>>
>>>>>>>>>
>>>>>>>>>> current set_rate method in clk-pll changes PLL register setting directly. Another
>>>>>>>>>> way uses FHCTL to change PLL rate.
>>>>>>>>>
>>>>>>>>> ...and of course, if we change that, we're effectively mutating the functionality
>>>>>>>>> of the MediaTek clk-pll driver and please understand that seeing a clear mutation
>>>>>>>>> in that driver is a bit more human-readable.
>>>>>>>>>
>>>>>>>>> Besides, this makes me think about one question: is there any instance in which,
>>>>>>>>> when FHCTL rate setting fails, we fall back to direct register writes?
>>>>>>>>>
>>>>>>>>> I don't think that this is feasible because we have a register in FHCTL that
>>>>>>>>> effectively hands over control to it, so direct register writes should not work
>>>>>>>>> when the PLL is not under APMIXEDSYS control, but I'm asking just to be extremely
>>>>>>>>> sure that my understanding is right.
>>>>>>>
>>>>>>> It won't fall back to direct register writes when FHCTL rate setting fails. But, PLL
>>>>>>> control mode will switch back to APMIXEDSYS after frequency hopping completed.
>>>>>>>
>>>>>>> There are two cases that we need to fall back to direct register writes:
>>>>>>>       1. PLL support FHCTL but it doesn't want to use FHCTL.
>>>>>>>       2. PLL doesn't support FHCTL HW.
>>>>>>>
>>>>>>
>>>>>> For case N.1, if this is board-specific, we have to resort to devicetree properties
>>>>>> that will enable/disable FHCTL on specific PLLs.
>>>>>>
>>>>>> mediatek,fhctl-disable = <CLK_APMIXED_MSDCPLL>, <CLK_APMIXED_NNAPLL>;
>>>>>>
>>>>>> mediatek,ssc-enable = <CLK_APMIXED_MFGPLL>, <CLK_APMIXED_TVDPLL>;
>>>>>>
>>>>>> These are just examples - I don't currently know if it's a better idea to have an
>>>>>> allowlist or a blocklist as devicetree properties, as that depends on the expected
>>>>>> number of PLLs for which we en/dis fhctl or just ssc (if we generally want fhctl
>>>>>> enabled on all but one PLLs, we should use fhctl-disable, otherwise, fhctl-enable).
>>>>>
>>>>> We also have a properity "ssc-rate" for setting up the ssc rate in percentage. The "ssc-
>>>>> rate" properity is under fhctl dts node and can be setup on each fhctl-PLL.
>>>>>
>>>>
>>>> Right. For that, we could have a default sensible percentage when SSC is enabled
>>>> but no rate is set in devicetree, or we can perhaps consider SSC enabled when any
>>>> meaningful SSC rate is set... For example:
>>>>
>>>> mediatek,ssc-enable = <CLK_APMIXED_MFGPLL>, <CLK_APMIXED_TVDPLL>;
>>>> mediatek,ssc-percent = <5>, <5>;
>>>>
>>>> ... or something like:
>>>>
>>>> mediatek,ssc = <CLK_APMIXED_MFGPLL 5>, <CLK_APMIXED_TVDPLL 5>;
>>>>
>>>> ...but I'd like to have some feedback on that from somebody else, as I don't know
>>>> if that would be acceptable in devicetree, or if there's any cleaner, niftier
>>>> solution.
>>>
>>> OK, we will use this:
>>>
>>> mediatek,hopping-ssc-percent = <CLK_APMIXED_MFGPLL 5>, <CLK_APMIXED_TVDPLL 5>;
>>>
>>
>> Looks good.
>>
>>>>
>>>>>>
>>>>>>>>>
>>>>>>>>>> We will set some PLL's frequency be controlled
>>>>>>>>>> by clk-pll and some are controlled by FHCTL.
>>>>>>>>>
>>>>>>>>> Another question: is this also changing on a per-board basis?
>>>>>>>>>
>>>>>>>>> (note: the pll names in the example are random and not specific to anything)
>>>>>>>>>
>>>>>>>>> Example: board A wants FHCTL on MMPLL, TVDPLL, MPLL, but *shall not* hand over
>>>>>>>>>                       NNAPLL, MFGPLL
>>>>>>>>>               board B wants FHCTL on NNAPLL, TVDPLL but *shall not* hand over MMPLL
>>>>>>>>>
>>>>>>>>> Granted that the two A, B boards are using the same SoC, can that ever happen?
>>>>>>>
>>>>>>> This could happen if A, B boards have different desense issue.
>>>>>>>
>>>>>>
>>>>>> Ok, so it's definitely board specific. Devicetree is the way to go for this.
>>>>>>
>>>>>>>>>
>>>>>>>>>> And use `perms` param to decide
>>>>>>>>>> whether a PLL is using FHCTL to change its frequency.
>>>>>>>>>
>>>>>>>>> The perms param seems to be about:
>>>>>>>>>       * Enabling debug (but you're not providing any way to actually use debugging
>>>>>>>>>         features, so what's the point?)
>>>>>>>
>>>>>>> Debugging feature is not used yet, we can removed it.
>>>>>>>
>>>>>>
>>>>>> If the debugging features of the FHCTL driver will be like what I can see on
>>>>>> the downstream MT6893 5.10 kernel, that's not really applicable to upstream.
>>>>>>
>>>>>> In that case, please remove the debug.
>>>>>
>>>>> Ok, we will remove it.
>>>>>
>>>>>>
>>>>>>>>>       * Handing over PLL control to FHCTL for hopping (can be as well done with
>>>>>>>>>         simply using a different .set_rate() callback instead of a flag)
>>>>>>>
>>>>>>> There has some PLL that have FHCTL but don't want to use FHCTL. The flag is used in
>>>>>>> this case.
>>>>>>>
>>>>>>
>>>>>> Use the flag to set the right .set_rate() callback, set at probe time, instead of
>>>>>> checking that flag at every set_rate() call.
>>>>>
>>>>> We will setup .set_rate() callback when doing fhctl-pll init.
>>>>>
>>>>>>
>>>>>>>>>       * Enabling/disabling Spread Spectrum Clocking (and I think that this is a
>>>>>>>>>         legit use for flags, but if it's just one flag, you can as well use a
>>>>>>>>>         bool and manage this with a devicetree param like "enable-ssc")
>>>>>>>>>
>>>>>>>>> That said, I think that the current way of enabling the FHCTL is more complicated
>>>>>>>>> than how it should really be.
>>>>>>>
>>>>>>> Here needs an option to decide whether to enable FHCTL-hopping or FHCTL-ssc since
>>>>>>> these two are per-board basis.
>>>>>>>
>>>>>>> We cannot force all PLL hand over to FHCTL for hopping casue not all PLLs support
>>>>>>> FHCTL and not all PLLs have need of using FHCTL-hopping.
>>>>>>>
>>>>>>
>>>>>> Board specific -> devicetree
>>>>>>
>>>>>> SoC specific -> hardcode, no devicetree.
>>>>>>
>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> FHCTL has another function called SSC(spread spectrum clocking) which is used to
>>>>>>>>>> solve PLL de-sense problem. De-sense problem is board-related so we introduce a
>>>>>>>>>> `ssc-rate` param in the devicetree to decide whether SSC is enabled and how many
>>>>>>>>>> rate should be set. Mixing SSC function into clk-pll may cause clk-pll more
>>>>>>>>>> complex.
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Thing is, I don't get why you think that adding SSC to clk-pll would complicate it
>>>>>>>>> so much... it's really just a few register writes and nothing else, so I really
>>>>>>>>> don't see where the problem is, here.
>>>>>>>>>
>>>>>>>>> Another issue is that this driver may be largely incomplete, so perhaps I can't
>>>>>>>>> really see the complications you're talking about? Is this the case?
>>>>>>>>>
>>>>>>>>> Regarding keeping the FHCTL code in separated files, that's fine, but I would still
>>>>>>>>> integrate it tightly in clk-pll and its registration flow, because - yes, this is
>>>>>>>>> for sure not mandatory, but the main parameters are constant, they never change for
>>>>>>>>> a specific PLL, as they're register offsets, bits and masks (which, again, will
>>>>>>>>> never change as long as we're using the same SoC).
>>>>>>>
>>>>>>> The driver may need to supoport microP by future HW design, standalone file clk-
>>>>>>> fhctl.c helps to trigger init flow of such as ap-init-flow, microP-init-flow .....,
>>>>>>> and those different init-flow also need to run some communication API with microP.
>>>>>>> Those communication APIs are not suitable to merge into clk-pll.
>>>>>>>
>>>>>>
>>>>>> Let's use clk-fhctl as an helper then, we can make sure to call the init flow for
>>>>>> the microP in the SoC-specific clock drivers, I think that's not a problem?
>>>>>>
>>>>>> clk_mtfuturesoc_someip_probe()
>>>>>> {
>>>>>> 	.... register clocks ....
>>>>>>
>>>>>> 	freqhopping_microp_init();
>>>>>>
>>>>>> 	return ret;
>>>>>> }
>>>>>>
>>>>>> If there's hardware out there that supports such feature and a downstream kernel to
>>>>>> look at, please tell me which one, so that I will be able to check it out and
>>>>>> perhaps understand how this flow works.
>>>>>>
>>>>>> P.S.: I guess it's not fhctl-sspm?
>>>>>
>>>>> You could find clk-fhctl-mcupm.c and clk-fhctl-gpueb.c on the downstream MT6893 5.10
>>>>> kernel. Those codes require the PLL hardware specification to determine which PLL
>>>>> group(eg. PLL TOP group, GPUEB group) runs on which microP and has responsibilty to
>>>>> communicate with the microP.
>>>>>
>>>>> If we implement these things into clk-pll driver, clk-pll driver not only needs to control
>>>>> PLL frequency but also needs to deal with microP IPI. It makes clk-pll driver have others
>>>>> works that is not belong to PLL operation. That's why we tend to have a standalone driver
>>>>> for FHCTL.
>>>>>
>>>>
>>>> Ok having something to analyze made this entire thing a bit more clear in my mind,
>>>> thanks for the pointers.
>>>>
>>>> Analyzing clk-fhctl-mcupm and clk-fhctl-gpueb makes me see that there's a lot of
>>>> common code between the two: x_hopping_v1(), x_ssc_enable_v1(), x_ssc_disable_v1()
>>>> (where x = {gpueb,mcupm}) are really the same functions, duplicated and renamed
>>>> and nothing else.
>>>> The only difference is the get_xxxx_ipidev(), which is avoidable by assigning
>>>> mboxes = <...something...> in devicetree (gpueb mailbox, or mcupm mailbox).
>>>>
>>>> Even the `FH_DEVCTL_CMD_ID` enumeration uses the same values!
>>>>
>>>> To unroll that riddle, I would at that point add a new MediaTek specific clock
>>>> driver (like clk-pll) and call it `clk-ipi.c`, because that's what it does in
>>>> the end: whatever we do, goes through a mailbox instead of a direct MMIO write.
>>>>
>>>> That clk-fhctl-ipi would contain a probe function that gets the mailbox handle,
>>>> then we would add something like `clk_fhctl_set_rate()` function, export it in
>>>> the `clk-mtk.h` or in a new `clk-fhctl.h` header, then assign the right callback
>>>> in either the SoC's clock driver (by registering a different clock type, which,
>>>> in this case, would be clk-fhctl-ipi instead of clk-pll), or in clk-pll itself...
>>>>
>>>> In the end, I'm effectively proposing to:
>>>>
>>>> 1. Merge the direct-MMIO handling of FHCTL in clk-pll;
>>>> 2. Create a new driver (and clock type, eventually) for the IPI handling of FHCTL.
>>>
>>>   From your idea, I think we can also create a new clock type for fhctl such as clk-pll-fh
>>> and add a new PLL register function for PLL+FHCTL. Then we can change the registery
>>> interface and won't affect the legacy ICs. Also, if FHCTL has changes, we only need to
>>> modify clk-pll-fh.
>>> I think using a new clock type has extendibility for FHCTL changes and also compatiable
>>> with legacy ICs.
>>>
>>> clk-pll.h
>>> 	/* Define FHCTL data structure and contains mtk_pll_data.
>>> 	 * We can use mtk_pll_data later. */
>>> 	mtk_pll_fh_data {
>>> 		struct mtk_pll_data pll_data;
>>> 		/* fhctl_data */
>>> 		unsigned int fh_id;
>>> 		unsigned int ssc_rate;
>>> 		...
>>> 	}
>>>
>>> clk-mt8186-apmixedsys.c
>>> 	func clk_mt8186_apmixed_probe()
>>> 		/* There are two implementations.
>>> 		 * If ICs need FHCTL such as MT8186, use mtk_clk_register_pllfhs()
>>> 		 * For those legacy ICs which don't need FHCTL, still use
>>> 		 * mtk_clk_register_plls().
>>> 		 */
>>> 		/* 1. Need FHCTL. Use API from clk-pll-fh.c */
>>> 		fhctl_parse_dt()
>>> 		mtk_clk_register_pllfhs(plls data, fh-plls data)
>>> 		
>>> 		/* 2. Legacy ICs. Use API from clk-pll.c */
>>> 		mtk_clk_register_plls()
>>
>> I'm not sure if we're saying the very same thing here, but for the sake of being
>> clear and avoiding any misunderstanding, here's my description.
>>
>>
>> We should call both functions: register_pllfhs() for the PLLs that have support for
>> freqhopping, register_plls() for the ones that *do not support* freqhopping.
>>
>> Example for PLL_A, PLL_B, PLL_C, PLL_D:
>>
>> Freqhopping supported (enabled or not): PLL_A, PLL_B
>> Freqhopping NOT supported at all: PLL_C, PLL_D
>>
>> fhplls_data[] = { PLL_A, PLL_B };
>> plls_data[] = { PLL_C, PLL_D };
>>
>> func mtk_clk_register_pllfhs(fhdata)
>> 	walk through fhplls_data only, other plls are not passed to this function
>>
>> func clk_mt8186_apmixed_probe()
>> 	/* Some PLLs must be controlled directly via MMIO, while others
>> 	 * support Frequency Hopping through FHCTL.
>> 	 * Where FHCTL is supported, register clock with register_pllfhs.
>> 	 * PLLs that are not supported by FHCTL: register with register_plls.
>> 	 */
>>
>> 	/* Register FHCTL PLLs */
>> 	fhctl_parse_dt()
>> 	mtk_clk_register_pllfhs(array of plls supporting pllfh)
>>
>> 	/* Register the PLLs that do not support FHCTL at all */
>> 	mtk_clk_register_plls(all the other PLLs that cannot be FHCTL-controlled)
>>
> 
> I have a different opinion here. I think we should just choose one register function when
> probe and it depends on platform implementation instead of a PLL is supported FHCTL or
> not. We have an option to use clk-pll-fh or clk-pll at the beginning of new IC
> development. And, we want it's easy to add FHCTL support on legecy ICs.
> 
> The way of how we use the register function is affected by the way we use fhplls_data. If
> FHCTL supported or not is used to decide which registery function should we use, it has to
> change the exist plls_data. But most of IC's PLL data is already exist. So I want to use a
> structure to descript FHCTL HW itself and have a link to existed PLL data.
> 
>  From your example, it will look like:
> 
> plls_data = { PLL_A, PLL_B, PLL_C, PLL_D };  /* Already existed */
> fhplls_data = { FH_A,
> FH_B };  /* New added for FHCTL data */
> 
> func mtk_clk_register_pllfhs(plls_data, fhplls_data)
> 	fhctl_match_pll_data()
> 		/* Link fhpll and pll:
> 		 *   FH_A -> PLL_A
> 		 *   FH_B -> PLL_B
> 		 */
> 
> For MT8186 and ICs need FHCTL supported:
> 	func clk_mt8186_apmixed_probe()
> 		fhctl_parse_dt()
> 		mtk_clk_register_pllfhs(plls_data, fhplls_data)
> 
> For those don't need FHCTL and legacy ICs:
> 	func clk_mtxxxx_apmixed_probe()
> 		mtk_clk_register_plls(plls_data)
> 
> When one ICs that need to support FHCTL but they didn't implement before, we only need to
> change the registery function and add FHCTL data, no need to modify existed plls_data. I
> think it can save our development time and maintenance effort.
> 

I see what you mean now. Okay, that seems sensible.

>>>
>>> clk-pll.c
>>> 	/* No functional changes, so legacy ICs won't be affected.
>>> 	 * Export clk_ops functions to clk-pll-fh.c
>>> 	 */
>>> 	func mtk_clk_register_plls()
>>> 		init.ops = &mtk_pll_ops;
>>>
>>> clk-pll-fh.c
>>> 	/* A clock type of FHCTL PLL. Used to setup HW data and ops.
>>> 	 * Most of ops functions inherit from clk-pll.c.
>>> 	 * If PLL not support or not enable FHCTL, fallback to use &mtk_pll_ops.
>>> 	 */
>>> 	func mtk_clk_register_pllfhs(plls data, fh-plls data)
>>> 		fhctl_match_pll_data()  /* match mtk_pll_data and mtk_pll_fh_data */
>>> 		fhctl_hw_init()
>>> 		if (fhctl_is_supported_and_enabled(pll))
>>
>> Overall, this seems to look good, minor one nit: if FHCTL is *not supported* on
>> a PLL, we should *not* even call mtk_clk_register_pllfhs on that PLL, so your
>> pseudocode would be just:
>>
>> 		if (fhctl_is_enabled(pll))
> 
> The requirements of clk-pll-fh are:
> 1. It is compatible with those PLLs that don't support FHCTL HW.
> 2. It can handle PLLs that supported FHCTL but aren't enabled.
> 3. It can handle PLLs that supported FHCTL but are enabled.
> 
> So, I use fhctl_is_supported_and_enabled(PLL) here. No matter a PLL supports FHCTL or not,
> it can work.
> 

Alright, let's go with that!

>>
>>> 			init.ops = &mtk_pll_fhctl_ops;
>>> 		else
>>> 			init.ops = &mtk_pll_ops;
>>> 	
>>> 		if (ssc_is_enable(pll))
>>> 			fhctl_ssc_enable(pll)
>>>
>>> clk-fhctl.c
>>> 	/* APIs of FHCTL HW operations */
>>> 	func fhctl_hw_init()
>>> 	func fhctl_hopping()
>>> 	func fhctl_ssc_enable()
>>>
>>>
>>
>> So it seems that we've reached an agreement here, this was a nice planning
>> discussion; we should now have a nice and solid base to work on, which is
>> great.
>>
>> Cheers,
>> Angelo
> 

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