Re: [PATCH 3/5] drm/rcar-du: dsc: Add rudimentary Renesas R-Car V4H DSC driver

[Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>]

Hi,

On 15/05/2026 11:05, Geert Uytterhoeven wrote:
> Hi Tomi,
> 
> On Fri, 15 May 2026 at 10:03, Tomi Valkeinen
> <tomi.valkeinen@ideasonboard.com> wrote:
>> On 15/05/2026 10:49, Geert Uytterhoeven wrote:
>>> On Thu, 14 May 2026 at 14:25, Tomi Valkeinen
>>> <tomi.valkeinen+renesas@ideasonboard.com> wrote:
>>>> From: Marek Vasut <marek.vasut+renesas@mailbox.org>
>>>>
>>>> The Renesas DSC Display Stream Compression is a bridge embedded in the
>>>> Renesas R-Car V4H SoC. The bridge performs VESA DSC encoding of up to
>>>> 8k or 400 Mpixel/s . Add rudimentary driver, which currently acts as a
>>>> pass-through bridge and allows DSI1 to be operational on R-Car V4H.
>>>>
>>>> Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
>>>> [tomi.valkeinen: use bridge->next_bridge, minor changes]
>>>> Signed-off-by: Tomi Valkeinen <tomi.valkeinen+renesas@ideasonboard.com>
>>>
>>> Thanks for your patch!
>>>
>>>> --- /dev/null
>>>> +++ b/drivers/gpu/drm/renesas/rcar-du/rcar_dsc.c
>>>
>>>> +
>>>> +static void rcar_dsc_atomic_enable(struct drm_bridge *bridge,
>>>> +                                  struct drm_atomic_state *state)
>>>> +{
>>>> +       struct rcar_dsc *dsc = bridge_to_rcar_dsc(bridge);
>>>> +
>>>> +       WARN_ON(clk_prepare_enable(dsc->clk));
>>
>> Ah, just missed your comment and sent the v2.
>>
>>> Who don't you use pm_runtime_resume_and_get() instead, like
>>> rcar_cmm.c? Then you don't need to get the clock at all, and the driver
>>
>> Hmm, why wouldn't I need to get the clock? What does the runtime PM do
>> on Renesas?
> 
> Runtime PM powers on the power domain (if present), and starts
> the device by enabling its module clock.
> 
>>> will keep on working if the DSC ever ends up in a power domain.
>> I can add runtime PM. I just felt that it was overcomplicating a "dummy"
>> driver that just needs to enable the clock when the video pipeline is
>> enabled.
> 
> Funny, I would say you are overcomplicating a dummy driver by adding
> explicit clock control ;-)
Well, now that I know the runtime PM does magics behind the scenes, you 
are right =).

How's "module clock" defined? Is it the first clock in the clocks DT 
property?

I'll have a look at whitehawk too. The funny thing is, I had a 
recollection that dsc was somehow used on whitehawk too. I looked at the 
board, and saw only the single mini DP connector on the CPU board, which 
already works, so I then concluded that the other DSI path is for the 
GMSL... I think I need new eyeglasses.

  Tomi