linux-kernel - Re: [RESEND PATCH] drm/tilcdc: fix raster control register setting

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Date:   Wed, 17 Feb 2021 18:45:07 +0100 (CET)
From:   Dario Binacchi <dariobin@...ero.it>
To:     Tomi Valkeinen <tomi.valkeinen@...asonboard.com>,
        linux-kernel@...r.kernel.org, Jyri Sarha <jyri.sarha@....fi>
Cc:     David Airlie <airlied@...ux.ie>, dri-devel@...ts.freedesktop.org
Subject: Re: [RESEND PATCH] drm/tilcdc: fix raster control register setting

Hi Tomi,

> Il 17/02/2021 07:41 Tomi Valkeinen <tomi.valkeinen@...asonboard.com> ha scritto:
> 
>  
> On 16/02/2021 22:22, Dario Binacchi wrote:
> > The fdd property of the tilcdc_panel_info structure must set the reqdly
> > bit field  (bit 12 to 19) of the raster control register. The previous
> > statement set the least significant bit instead.
> > 
> > Signed-off-by: Dario Binacchi <dariobin@...ero.it>
> > 
> > ---
> > 
> >  drivers/gpu/drm/tilcdc/tilcdc_crtc.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/tilcdc/tilcdc_crtc.c b/drivers/gpu/drm/tilcdc/tilcdc_crtc.c
> > index 30213708fc99..238068e28729 100644
> > --- a/drivers/gpu/drm/tilcdc/tilcdc_crtc.c
> > +++ b/drivers/gpu/drm/tilcdc/tilcdc_crtc.c
> > @@ -393,7 +393,7 @@ static void tilcdc_crtc_set_mode(struct drm_crtc *crtc)
> >  			return;
> >  		}
> >  	}
> > -	reg |= info->fdd < 12;
> > +	reg |= info->fdd << 12;
> >  	tilcdc_write(dev, LCDC_RASTER_CTRL_REG, reg);
> >  
> >  	if (info->invert_pxl_clk)
> > 
> 
> This is interesting, looks like this has always been broken, and in many
> cases sets bits 0, which is the enable bit. So we enable LCDC before
> even setting the fb address. How does this not blow up LCDC totally?
> 
> The fix looks correct to me, but it will change the register value for
> boards that have apparently been working for years.
> 
> Dario, did you test this on actual HW, or did you just spot the error?

I tested it on Beaglebone Black + LCD cape (4.3inch).
I also checked the register value with devmem.

Regards,
Dario

> 
> Reviewed-by: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
> 
>  Tomi
> _______________________________________________
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> dri-devel@...ts.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

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