[PATCH 2/4] drm/rcar-du: dsi: Remove fixed PPI lane count setup

[Tomi Valkeinen]

Hi,

On 12/08/2025 22:35, Marek Vasut wrote:
> On 8/12/25 3:30 PM, Tomi Valkeinen wrote:
> 
> Hi,
> 
>>>> diff --git a/drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi_regs.h b/
>>>> drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi_regs.h
>>>> index b3e57217ae63..cefa7e92b5b8 100644
>>>> --- a/drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi_regs.h
>>>> +++ b/drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi_regs.h
>>>> @@ -80,10 +80,7 @@
>>>>    * PHY-Protocol Interface (PPI) Registers
>>>>    */
>>>>   #define PPISETR                0x700
>>>> -#define PPISETR_DLEN_0            (0x1 << 0)
>>>> -#define PPISETR_DLEN_1            (0x3 << 0)
>>>> -#define PPISETR_DLEN_2            (0x7 << 0)
>>>> -#define PPISETR_DLEN_3            (0xf << 0)
>>>> +#define PPISETR_DLEN_MASK        (0xf << 0)
>>>>   #define PPISETR_CLEN            BIT(8)
>>>
>>> Looks fine, but do you know what the TXSETR register does? It also has
>>> LANECNT, but I don't see the driver touching that register at all.
>>> TXSETR:LANECNT default value is 3 (4 lanes), which matches with the old
>>> hardcoded behavior for PPISETR... So I wonder if that register should
>>> also be set?
>>
>> Ah, never mind, I now saw the patch 3 =). But should it be before patch
>> 2? Hmm, I guess that ordering is no better. Should they be combined into
>> "support 1,2,3 datalanes" patch?
> I think each patch fixes slighly different issue, even if the issues are
> related. I tried to keep the issue description in each patch commit
> message for posterity. I can squash them if you think that's better, I
> don't mind either way.

I was thinking about this the user's or backporting point of view.
Neither of the commits (clearly) say that they add support for 1/2/3
lane modes. You say they "fix", but they're not quite fixes either. The
patch 3 could be considered a fix, but at the moment it just writes the
default value to the register, so no point in marking it as a fix to be
backported.

So... I don't have a strong opinion, but I think a single patch that
adds support to 1, 2,3 lanes makes most sense.

 Tomi