Message-ID: <nvgm2jeyhabxdhurcflc2gu4vdk2zjfoba22mc6j3d7azxdicz@ln5pu676b3lf>
Date: Thu, 28 Aug 2025 13:31:45 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Ram Prakash Gupta <quic_rampraka@...cinc.com>
Cc: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Sachin Gupta <quic_sachgupt@...cinc.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Ulf Hansson <ulf.hansson@...aro.org>, linux-arm-msm@...r.kernel.org,
        linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org,
        quic_cang@...cinc.com, quic_nguyenb@...cinc.com,
        quic_bhaskarv@...cinc.com, quic_mapa@...cinc.com,
        quic_nitirawa@...cinc.com, quic_sartgarg@...cinc.com
Subject: Re: [PATCH V2 2/2] mmc: sdhci-msm: Rectify DLL programming sequence
 for SDCC

On Thu, Aug 28, 2025 at 01:30:21PM +0530, Ram Prakash Gupta wrote:
> 
> On 8/21/2025 7:45 PM, Ram Prakash Gupta wrote:
> > On 8/9/2025 3:10 PM, Dmitry Baryshkov wrote:
> >> On Thu, Aug 07, 2025 at 01:28:28AM +0530, Ram Prakash Gupta wrote:
> >>> On 7/31/2025 7:49 PM, Dmitry Baryshkov wrote:
> >>>> On 31/07/2025 14:46, Ram Prakash Gupta wrote:
> >>>>> On 7/30/2025 11:26 PM, Dmitry Baryshkov wrote:
> >>>>>> On Wed, Jul 23, 2025 at 03:43:37PM +0530, Ram Prakash Gupta wrote:
> >>>>>>> On 1/22/2025 3:20 PM, Dmitry Baryshkov wrote:
> >>>>>>>> On Wed, Jan 22, 2025 at 02:57:59PM +0530, Sachin Gupta wrote:
> >>>>>>>>> On 1/7/2025 8:38 PM, Dmitry Baryshkov wrote:
> >>>>>>>>>> On Tue, Jan 07, 2025 at 11:13:32AM +0530, Sachin Gupta wrote:
> >>>>>>>>>>> On 12/27/2024 12:23 AM, Dmitry Baryshkov wrote:
> >>>>>>>>>>>> On Thu, Dec 26, 2024 at 11:22:40AM +0530, Sachin Gupta wrote:
> >>>>>>>>>>>>> On 12/19/2024 11:24 AM, Dmitry Baryshkov wrote:
> >>>>>>>>>>>>>> On Wed, Dec 18, 2024 at 02:40:57PM +0530, Sachin Gupta wrote:
> >>>>>>>>>>>>>>> +
> >>>>>>>>>>>>>>> +static unsigned int sdhci_msm_get_clk_rate(struct sdhci_host *host, u32 req_clk)
> >>>>>>>>>>>>>>> +{
> >>>>>>>>>>>>>>> +    struct sdhci_pltfm_host *pltfm_host = sdhci_priv(host);
> >>>>>>>>>>>>>>> +    struct sdhci_msm_host *msm_host = sdhci_pltfm_priv(pltfm_host);
> >>>>>>>>>>>>>>> +    struct clk *core_clk = msm_host->bulk_clks[0].clk;
> >>>>>>>>>>>>>>> +    unsigned int sup_clk;
> >>>>>>>>>>>>>>> +
> >>>>>>>>>>>>>>> +    if (req_clk < sdhci_msm_get_min_clock(host))
> >>>>>>>>>>>>>>> +        return sdhci_msm_get_min_clock(host);
> >>>>>>>>>>>>>>> +
> >>>>>>>>>>>>>>> +    sup_clk = clk_round_rate(core_clk, clk_get_rate(core_clk));
> >>>>>>>>>>>>>>> +
> >>>>>>>>>>>>>>> +    if (host->clock != msm_host->clk_rate)
> >>>>>>>>>>>>>>> +        sup_clk = sup_clk / 2;
> >>>>>>>>>>>>>>> +
> >>>>>>>>>>>>>>> +    return sup_clk;
> >>>>>>>>>>>>>> Why?
> >>>>>>>>>>>>> Sorry, I did not understand your question. Can you please explain in detail.
> >>>>>>>>>>>> Please explain the maths. You get the rate from the clock, then you
> >>>>>>>>>>>> round it, but it is the rate that has just been returned, so there
> >>>>>>>>>>>> should be no need to round it. And after that there a division by two
> >>>>>>>>>>>> for some reason. So I've asked for an explanation for that code.
> >>>>>>>>>>>>
> >>>>>>>>>>> clk_round_rate is used in case of over clocking issue we can round it to the
> >>>>>>>>>>> usable frequency.
> >>>>>>>>>> If it is a frequency _returned_ by the clock driver, why do you need to
> >>>>>>>>>> round it? It sounds like that freq should be usable anyway.
> >>>>>>>>>>
> >>>>>>>>> I agree, rounding will be taken care by clock driver. Will remove in my next
> >>>>>>>>> patch.
> >>>>>>>>>
> >>>>>>>>>>> Divide by 2 is used as for HS400 the tuning happens in
> >>>>>>>>>>> HS200 mode only so to update the frequency to 192 Mhz.
> >>>>>>>>>> Again, is it really 192 MHz? Or 19.2 MHz?
> >>>>>>>>>> Also if it is for HS400, then shouldn't /2 be limited to that mode?
> >>>>>>>>>>
> >>>>>>>>> Yes, It is 192 MHz.
> >>>>>>>> Good, thanks for the confirmation.
> >>>>>>>>
> >>>>>>>>> As part of eMMC Init, driver will try to init with the best mode supported
> >>>>>>>>> by controller and device. In this case it is HS400 mode, But as part of
> >>>>>>>>> HS400 mode, we perform Tuning in HS200 mode only where we need to configure
> >>>>>>>>> half of the clock.
> >>>>>>>> This isn't an answer to the question. Let me rephrase it for you: if the
> >>>>>>>> /2 is only used for HS400, why should it be attempted in all other
> >>>>>>>> modes? Please limit the /2 just to HS400.
> >>>>>>> Hi Dmitry,
> >>>>>>>
> >>>>>>> like updated earlier by Sachin, HS400 tuning happens in HS200 mode, so if
> >>>>>>> we try to use "ios->timing == MMC_TIMING_MMC_HS400" that wont help, as at
> >>>>>>> this stage timing can be MMC_TIMING_MMC_HS200/MMC_TIMING_MMC_HS400 for
> >>>>>>> hs200 tuning and hs400 selection. In this case we must divide clk by 2
> >>>>>>> to get 192MHz and we find this as host->clock wont be equal to
> >>>>>>> msm_host->clk_rate.
> >>>>>> What are host->clock and msm_host->clk_rate at this point?
> >>>>>> What is the host->flags value? See sdhci_msm_hc_select_mode().
> >>>>> There are 2 paths which are traced to this function when card initializes
> >>>>> in HS400 mode, please consider below call stack in 2 paths
> >>>>>
> >>>>> sdhci_msm_configure_dll
> >>>>> sdhci_msm_dll_config
> >>>>> sdhci_msm_execute_tuning
> >>>>> mmc_execute_tuning
> >>>>> mmc_init_card
> >>>>> _mmc_resume
> >>>>> mmc_runtime_resume
> >>>>>
> >>>>> with values of host->clock as 200000000 & msm_host-clk_rate as 400000000
> >>>> Please check the rates explicitly in the code rather than just checking that they are not equal.
> >>> in function msm_get_clock_mult_for_bus_mode(), clk multiplier returns 2, with HS400
> >>> DDR52 and DDR50 modes which is called from sdhci_msm_set_clock() and
> >>> sdhci_msm_execute_tuning. And in sdhci_msm_execute_tuning(), we are calling
> >>> sdhci_msm_dll_config() when SDHCI_HS400_TUNING is set and this flag is cleared
> >>> immediately after return. And sdhci_msm_dll_config() is called after that.
> >>>
> >>> Now when the card is supporting HS400 mode, then from mmc_hs200_tuning(),
> >>> sdhci_prepare_hs400_tuning is getting called, and there SDHCI_HS400_TUNING
> >>> flag is set, and clock set is multiplying the clk rate by 2 in below call stack
> >>>
> >>> msm_set_clock_rate_for_bus_mode
> >>> sdhci_msm_execute_tuning
> >>> mmc_execute_tuning
> >>> mmc_init_card
> >>>
> >>> so this clk rate is doubling only with HS400 mode selection and while setting up
> >>> dll in HS400 dll configuration path sup_clk need to divide by 2 as msm_host->clk_rate
> >>> is twice the host->clock as mentioned above.
> >> I don't see how it's relevant. I'm asking you to check for the rate
> >> values explicitly in the driver code rather than just checking that
> >> rateA != rateB. You might error out if rateA != rateB and they are not
> >> 192 MHz / 384 MHz
> > ok I see, but I got one another alternate to this, I can try use similar checks used in
> > function msm_get_clock_mult_for_bus_mode(), ios.timing == MMC_TIMING_MMC_HS400 
> > host->flags & SDHCI_HS400_TUNING, but for this I ll have to move check
> > host->flags &= ~SDHCI_HS400_TUNING in function sdhci_msm_execute_tuning () at the bottom
> > of this function, this will make code more readable and consistent to checks at other
> > places but I am testing it right now and will update.
> >
> > If this doesn't work then I ll explicitly use the rate value in check.
> >
> > Thanks,
> > Ram
> 
> Hi Dmitry,
> 
> adding checks for ios.timing == MMC_TIMING_MMC_HS400 && host->flags & SDHCI_HS400_TUNING
> serves the same purpose for dividing the clk when mode is hs400 and hs400_tuning flag is
> set, and clk value checks can be avoided now.
> 
> With this HS200, HS400, HS400ES modes of eMMC is tested.
> 
> so if this approach looks good to you, then I would like to proceed with next patchset.

LGTM.


-- 
With best wishes
Dmitry

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