Re: [RFC 14/21] v4l: vsp1: Change VSP1 LIF linebuffer FIFO

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Eugeniu,

On Thu, Apr 21, 2022 at 06:12:59PM +0200, Eugeniu Rosca wrote:
> Dear Uli,
> Dear Laurent,
> Dear Renesas community,
> 
> On Mo, Mai 30, 2016 at 06:00:13 +0200, Ulrich Hecht wrote:
> > This patch changes to VSPD hardware recommended value.
> > Purpose is highest pixel clock without underruns.
> > In the default R-Car Linux BSP config this value is
> > wrong and therefore there are many underruns.
> > 
> > Signed-off-by: Takashi Saito <takashi.saitou.ry@renesas.com>
> > Signed-off-by: Koji Matsuoka <koji.matsuoka.xm@renesas.com>
> > Signed-off-by: Ulrich Hecht <ulrich.hecht+renesas@gmail.com>
> > Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
> > ---
> >  drivers/media/platform/vsp1/vsp1_lif.c | 6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> Apologize for reviving this very old thread.
> 
> We've been struggling with very rare and difficult to reproduce
> display flickering occurrences and, after significant amount of
> troubleshooting and debugging, with some support from Renesas,
> we've been able to identify that those flicker issues are caused
> by VSPD underruns.
> 
> What we've also learned is that one possible root-cause for seeing
> VSPD underruns is having wrong QoS settings in DBSC (set in ATF).
> 
> What was particularly helpful in identifying the underruns themselves
> is Renesas BSP commit [1], whose discussions we were unable to track
> on linux-renesas-soc LKML.
> 
> My question is very simple. Since the meat of the Renesas patch [1]
> is basically a printk in the interrupt context and an array storing
> the total number of underruns occurred since startup, would you be
> willing to review the refactored version of this patch on LKML?
> 
> In that case, we'll definitely invest some time to upstream it.

Absolutely ! I'm all for helping debugging.

> Thank you for your attention and feedback.
> 
> [1] https://github.com/renesas-rcar/linux-bsp/commit/12ea79975a10f
>     ("v4l: vsp1: Add underrun debug messege option")

-- 
Regards,

Laurent Pinchart