Re: [RESEND PATCH v6 17/20] drm/mediatek: Support MT8188 Padding in display driver

[AngeloGioacchino Del Regno]

Il 28/09/23 05:39, Shawn Sung (宋孝謙) ha scritto:
> Hi CK,
>
> On Thu, 2023-09-28 at 03:05 +0000, CK Hu (胡俊光) wrote:
> > Hi, Hsiao-chien:
> >
> > On Mon, 2023-09-11 at 15:42 +0800, Hsiao Chien Sung wrote:
> > > Padding is a new display module on MT8188, it provides ability
> > > to add pixels to width and height of a layer with specified colors.
> > >
> > > Due to hardware design, Mixer in VDOSYS1 requires width of a layer
> > > to be 2-pixel-align, or 4-pixel-align when ETHDR is enabled,
> > > we need Padding to deal with odd width.
> > >
> > > Please notice that even if the Padding is in bypass mode,
> > > settings in register must be cleared to 0,
> > > or undefined behaviors could happen.
> >
> > You just set padding to bypass mode and not clear settings to 0. Any
> > thing wrong?
>
> Since the deafult value of all the registers in Padding is zero, and
> we are not using Padding currently, it's fine if we just set padding to
> bypass mode witout clearing other registers.
>
> The comment is just a reminder in case we forget it in the future.

Do *not* rely on default register values, because you don't know what booted
Linux in the first place: you shall *not* expect a clean state and you shall
*not* expect a clean boot.

Besides, what I see is that you're setting GENMASK(1, 0) without explaining
why in the code: you have to add at least the definitions for PADDING_EN and
PADDING_BYPASS.

I also don't see why you shouldn't add at least basic handling for this block,
as it looks easy enough: after all, you anyway have to make sure that the
registers are cleared - might as well just add a little more effort on top
and actually set them to meaningful values? That's ultimately your choice, but
I don't want to see any GENMASK(31,0) write even for register clearing.

Please make this driver proper.

Thanks,
Angelo

> Regards,
> Hsiao Chien Sung