Message-ID: <84e688fed290a112b3a95767c5ee1f0e5677ac06.camel@mediatek.com>
Date: Thu, 28 Nov 2024 03:08:35 +0000
From: CK Hu (胡俊光) <ck.hu@...iatek.com>
To: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	"chunkuang.hu@...nel.org" <chunkuang.hu@...nel.org>
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Subject: Re: [PATCH v1 6/6] drm/mediatek: Add support for MT8195 Digital
 Parallel Interface

On Wed, 2024-11-27 at 13:44 +0100, AngeloGioacchino Del Regno wrote:
> External email : Please do not click links or open attachments until you have verified the sender or the content.
> 
> 
> Il 27/11/24 10:04, CK Hu (胡俊光) ha scritto:
> > On Wed, 2024-11-27 at 09:41 +0100, AngeloGioacchino Del Regno wrote:
> > > External email : Please do not click links or open attachments until you have verified the sender or the content.
> > > 
> > > 
> > > Il 27/11/24 08:02, CK Hu (胡俊光) ha scritto:
> > > > On Tue, 2024-11-26 at 10:25 +0100, AngeloGioacchino Del Regno wrote:
> > > > > External email : Please do not click links or open attachments until you have verified the sender or the content.
> > > > > 
> > > > > 
> > > > > Il 26/11/24 04:07, CK Hu (胡俊光) ha scritto:
> > > > > > On Mon, 2024-11-25 at 17:55 +0100, AngeloGioacchino Del Regno wrote:
> > > > > > > External email : Please do not click links or open attachments until you have verified the sender or the content.
> > > > > > > 
> > > > > > > 
> > > > > > > Il 22/11/24 08:23, CK Hu (胡俊光) ha scritto:
> > > > > > > > Hi, Angelo:
> > > > > > > > 
> > > > > > > > On Wed, 2024-11-20 at 13:44 +0100, AngeloGioacchino Del Regno wrote:
> > > > > > > > > External email : Please do not click links or open attachments until you have verified the sender or the content.
> > > > > > > > > 
> > > > > > > > > 
> > > > > > > > > Add support for the DPI block found in the MT8195 and MT8188 SoCs.
> > > > > > > > > Inside of the SoC, this block is directly connected to the HDMI IP.
> > > > > > > > 
> > > > > > > > In MT8173, DPI0 is directly connected to HDMI.
> > > > > > > > The first version of this driver is just for MT8173 DPI0.
> > > > > > > > Does MT8173 DPI0 need this modification?
> > > > > > > > Or this modification is just for MT8188 and MT8195, then the description should be more than 'directly connected'.
> > > > > > > > 
> > > > > > > 
> > > > > > > This is only for MT8188 and MT8195, and MT8173 does *not* need any modification.
> > > > > > > 
> > > > > > > Please, what would you like to see in the description of this commit?
> > > > > > 
> > > > > > This patch does four jobs.
> > > > > > 
> > > > > > 1. Enable/disable tvd_clk for MT8195/MT8188 DPI.
> > > > > > 2. Do not set pixel clock for MT8195/MT8188 DPI.
> > > > > > 3. New DPI_INPUT_XXX and DPI_OUTPUT_XXX control for MT8195/MT8188 DPI.
> > > > > > 4. Do not power on/off for MT8195/MT8188 DPI.
> > > > > > 
> > > > > > Maybe you should break into 4 patches and each one has different reason.
> > > > > 
> > > > > Yeah I thought about that as well, but there's a fundamental issue with splitting
> > > > > the thing in multiple patches...
> > > > > 
> > > > > For enabling the tvd_clk in a separate patch, there's no problem - however, for the
> > > > > others....
> > > > > 
> > > > > 1. We need to introduce support for MT8195/88 DPI-HDMI, or the other patches would
> > > > >       not make sense (nor apply, anyway); then
> > > > > 2. We stop setting pixel clock with another patch; then
> > > > > 3. we don't power on/off, etc etc
> > > > > 
> > > > > The problem with doing it like so is that the patch #1 that I described would be
> > > > > introducing *faulty code*, because the support for that really depends on all of
> > > > > the others being present (otherwise the block won't work correctly).
> > > > > 
> > > > > So... if you want, I can easily split out the tvd_clk enable/disable, but splitting
> > > > > the rest wouldn't be clean.
> > > > > 
> > > > > Besides, keep in mind that... actually... for anything else that is not MT8195/88
> > > > > DPI0 (so, for other SoCs' DPI and for 95/88 DPINTF) the tvd_clk is already getting
> > > > > enabled by its child.. so, for those ones, a call to enable tvd_clk does exactly
> > > > > nothing apart from incrementing (enable) or decrementing (disable) the refcount for
> > > > > this clock by 1.
> > > > > 
> > > > > This means that the enablement/disablement of tvd_clk is actually important only
> > > > > for the MT8195/88 DPI and has literally no effect on anything else that is
> > > > > currently supported by the mtk_dpi driver anyway.
> > > > > 
> > > > > Still - if you want me to split out the tvd_clk en/dis patch, just confirm and I
> > > > > will split that one out...
> > > > > 
> > > > > > 
> > > > > > For #1 and #2, I've not reviewed the HDMI driver. Is the clock control influenced by new HDMI driver.
> > > > > 
> > > > > It kinda is - the HDMI-TX block gets its clock from the HDMI PHY's clock gen,
> > > > > but eventually it is the HDMI driver that tells to the PHY driver what clock it
> > > > > actually wants.
> > > > > 
> > > > > For #1, clk_prepare_enable() is ungating the clock that would otherwise gate the
> > > > > PHY's PLL output to the HDMI block.
> > > > > 
> > > > > > If it is software reason, maybe we can modify the new HDMI driver and make DPI driver consistent with MT8173.
> > > > > > If it is hardware reason. just describe the hardware reason.
> > > > > 
> > > > > Alright - the hardware reason is that the HDMIPHY generates the clock for the HDMI
> > > > > TX block, and that enabling the clock assigned to tvd_clk is necessary to ungate
> > > > > the PHY's ckgen output to the HDMI-TX (and I think - but not sure as I haven't
> > > > > analyzed that yet - that HDMI-RX should have the same gating technique, but that's
> > > > > definitely out of scope for this submission).
> > > > 
> > > > I think tvd_clk is the clock source of DPI, HDMI, and HDMI-PHY, so these hardware could work in the same frequency.
> > > > That means drivers of DPI, HDMI, and HDMI-PHY are equal to control tvd_clk.
> > > > In MT8173. software choose DPI driver to control tvd_clk.
> > > > In MT8195, software choose HDMI-PHY driver to control tvd_clk.
> > > 
> > > Yes, but in MT8195 the tvd is gated by a clock that is controller by the HDMI
> > > driver only, and not by the PHY - so, PHY sets the frequency, mtk_hdmi_v2 ungates
> > > that to the HDMITX block (with clk_prepare_enable(tvd_clk)).
> > > 
> > > > 
> > > > I would like to have the same control flow.
> > > > If "HDMI-PHY driver to control tvd_clk" is better, we could temporarily let MT8195 has different flow with MT8173.
> > > > So, is "HDMI-PHY driver to control tvd_clk" better?
> > > > 
> > > 
> > > I'm not sure I understand this last part, can you please rephrase?
> > 
> > I would like MT8173 and MT8195 has the same control flow, so keep DPI driver to control tvd_clk in MT8195.
> > If it's better to control tvd_clk by HDMI-PHY driver, both MT8173 and MT8195 control tvd_clk by HDMI-PHY driver.
> > But we are not able to test MT8173. So MT8173 keep control tvd_clk by DPI driver.
> > So control tvd_clk by HDMI-PHY driver is better?
> > 
> 
> Oh. Okay now I understand what you mean.
> 
> Unfortunately, we cannot control the tvd->hdmi gate from the PHY driver... this is
> because we do really rely on a specific ungate sequence, and the DPI driver really
> does need to control the gating of that CG on its own: when we want to bring up the
> DPI+HDMI, we need to:
>   - Start with *gated* clocks, so HW is OFF;
>   - Call mtk_dpi_bridge_enable() (done by drm framework);
>     - There, we now *ungate* the clocks
>     - DPI HW is ON -> we reset and write config to DPI registers
>       with function mtk_dpi_set_display_mode()
>     - We enable the DPI output (set EN in DPI_EN register)
> 
> If we move the CG to HDMI PHY, then we have to phy_configure() and phy_enable()
> inside of the DPI driver, which is also not really possible and can only be done
> in the HDMI driver - and that's because the HDMI driver reads EDID from DDC,
> which gives us the wanted pixel clock, and feeds it to the PHY.
> 
> In short, there's no way around that, the gating cannot be moved out of DPI driver.
> 
> > > 
> > > > > 
> > > > > > 
> > > > > > For #4, I don't know why DPI do not control power by its self?
> > > > > > Even though other driver may control the same power, power manager has reference count,
> > > > > > so each driver could control the same power by its self.
> > > > > 
> > > > > #4 is there both for a SW and for a HW reason.
> > > > > 
> > > > > The HW reason is that the DPI shall be powered on in a specific sequence in regard
> > > > > to HDMI-TX, due to the setup that is required by both (and ungating clocks before
> > > > > full configuration happens would lock up the hw block).
> > > > > 
> > > > > The SW reason is that mtk_crtc.c calls mtk_crtc_ddp_hw_init()->mtk_ddp_comp_start()
> > > > > in its .atomic_enable() callback, which happens in the wrong sequence in regard to
> > > > > HDMI because of the "natural" components order in the DRM framework (for MT8195/88!
> > > > > because for the others it either is the inverse or it does not matter - so for
> > > > > performance it's okay for it to be like that both on older SoCs and on DPINTF for
> > > > > 95/88) and this means that we *must not* call dpi_power_on() at that time but
> > > > > we must rather follow the atomic_enable()/bridge_enable() order imposed by DRM
> > > > > *also* for the clock en/dis calls in DPI.
> > > > 
> > > > It looks like the #4 could be a separate patch.
> > > > The commit message is what you describe here.
> > > > And
> > > > 
> > > > if (!dpi->conf->support_hdmi_power_sequence)
> > > >        mtk_dpi_power_on();
> > > > 
> > > 
> > > This means that I'd have to introduce the "hdmi power sequence" before actually
> > > introducing the real support for MT8195 HDMI....
> > > I honestly don't like that "too much", but it's fine, I don't have *too strong*
> > > opinions about that, so I will separate #4 as you suggested for v2.
> > 
> > This DPI series modification is all about HDMI.
> > Maybe merge this series with HDMI series and let the HDMI part in front of DPI part and it's more reasonable.
> > 
> 
> I have sent the two separately only because I thought it'd be easier for you to
> review them .. well, separately.
> But .. yes, this series is 99% about HDMI - the only thing that's not related to
> HDMI is patch [3/6] which is just a cleanup...
> 
> So if you want I can merge the two series into one, that's not a problem at all;
> in that case, do you want me to keep the patches as they are, or do you want me
> to still split #4 away from this patch?

I think each part would use a different config variable to show which code is related to which part.
So #4 could keep in this patch.
The commit message should describe all these parts.

If breakdown, it would be:

Patch 1: Add config variable 1
Patch 2: Add config variable 2
...
Patch n: Add support for MT8195 DPI support (add MT8195 config table)

Both combine into one patch or breakdown to multiple patch is OK for me.

Regards,
CK

> 
> > Regards,
> > CK
> > 
> > > 
> > > Cheers,
> > > Angelo
> > > 
> > > > Regards,
> > > > CK
> > > > 
> > > > > 
> > > > > Cheers,
> > > > > Angelo
> > > > > 
> > > > > > 
> > > > > > Regards,
> > > > > > CK
> > > > > > 
> > > > > > 
> > > > > > > 
> > > > > > > Cheers,
> > > > > > > Angelo
> > > > > > > 
> > > > > > > > Regards,
> > > > > > > > CK
> > > > > > > > 
> > > > > > > > > 
> > > > > > > > > Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
> > > > > > > > > ---
> > > > > > > 
> > > > > > > 
> > > > > 
> > > > > 
> > > > > 
> > > 
> > > 
> > > 
> 
> 

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