Re: [EXT] Re: [v1] drm/arm/mali-dp: Disable checking for required pixel clock rate

[Robin Murphy]

On 16/05/2019 10:42, Wen He wrote:
> > -----Original Message-----
> > From: Robin Murphy [mailto:robin.murphy@xxxxxxx]
> > Sent: 2019å5æ16æ 1:14
> > To: Wen He <wen.he_1@xxxxxxx>; dri-devel@xxxxxxxxxxxxxxxxxxxxx;
> > linux-kernel@xxxxxxxxxxxxxxx; liviu.dudau@xxxxxxx
> > Cc: Leo Li <leoyang.li@xxxxxxx>
> > Subject: [EXT] Re: [v1] drm/arm/mali-dp: Disable checking for required pixel
> > clock rate
> >
> > Caution: EXT Email
> >
> > On 15/05/2019 03:42, Wen He wrote:
> > > Disable checking for required pixel clock rate if ARCH_LAYERSCPAE is
> > > enable.
> > >
> > > Signed-off-by: Alison Wang <alison.wang@xxxxxxx>
> > > Signed-off-by: Wen He <wen.he_1@xxxxxxx>
> > > ---
> > > change in description:
> > >        - This check that only supported one pixel clock required clock rate
> > >        compare with dts node value. but we have supports 4 pixel clock
> > >        for ls1028a board.
> > >    drivers/gpu/drm/arm/malidp_crtc.c | 2 ++
> > >    1 file changed, 2 insertions(+)
> > >
> > > diff --git a/drivers/gpu/drm/arm/malidp_crtc.c
> > > b/drivers/gpu/drm/arm/malidp_crtc.c
> > > index 56aad288666e..bb79223d9981 100644
> > > --- a/drivers/gpu/drm/arm/malidp_crtc.c
> > > +++ b/drivers/gpu/drm/arm/malidp_crtc.c
> > > @@ -36,11 +36,13 @@ static enum drm_mode_status
> > > malidp_crtc_mode_valid(struct drm_crtc *crtc,
> > >
> > >        if (req_rate) {
> > >                rate = clk_round_rate(hwdev->pxlclk, req_rate);
> > > +#ifndef CONFIG_ARCH_LAYERSCAPE
> >
> > What about multiplatform builds? The kernel config doesn't tell you what
> > hardware you're actually running on.
>
> Hi Robin,
>
> Thanks for your reply.
>
> In fact, Only one platform integrates this IP when CONFIG_ARCH_LAYERSCAPE is set.
> Although this are not good ways, but I think it won't be a problem under multiplatform builds.

My point is that ARCH_LAYERSCAPE is going to be enabled in distribution 
kernels along with everything else, so you're effectively removing this 
check for all other vendors' Mali-DP implementations as well, which is 
probably not OK.

Furthermore, if LS1028A really only supports 4 specific modes as the BSP 
documentation I found claims, then surely you'd want a *more* specific 
check here, rather than no check at all?

Robin.