Re: [PATCH v1 6/6] drm/mediatek: Add support for MT8195 Digital Parallel Interface

[CK Hu (胡俊光)]

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.

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?

> 
> > 
> > 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();

Regards,
CK

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