On Fri, Mar 20, 2026 at 09:04:17AM +0100, Marco Felsch wrote: > On 26-03-20, Marek Vasut wrote: > > On 3/19/26 12:45 PM, Krzysztof Hałasa wrote: > > > Running (and terminating) Weston on i.MX8MP sometimes produced black > > > or grey screens. The LCDIF3 INT_STATUS_D0 register showed a FIFO underrun: > > > > > > 32FC6024: 1000002 > > > > > > The PANIC0_THRES register was set to: > > > > > > 32FC6238: AA0154 > > > > > > which apparently meant low = 2736 bytes (0xAA * 16 + 16), high = 5456 > > > bytes > > > (0x154 * 16 + 16). > > > > > > With this patch (based on NXP's driver) the watermarks are only 16 bytes > > > higher (register values increased by 1) and the underruns are gone. > > > > > > Tested on Solidrun Hummingboard Mate with a 1080p60 HDMI display. > > > > > > Signed-off-by: Krzysztof Hałasa <[email protected]> > > > > > > --- a/drivers/gpu/drm/mxsfb/lcdif_kms.c > > > +++ b/drivers/gpu/drm/mxsfb/lcdif_kms.c > > > @@ -353,8 +353,8 @@ static void lcdif_enable_controller(struct > > > lcdif_drm_private *lcdif) > > > u32 reg; > > > /* Set FIFO Panic watermarks, low 1/3, high 2/3 . */ > > > - writel(FIELD_PREP(PANIC0_THRES_LOW_MASK, 1 * PANIC0_THRES_MAX / 3) | > > > - FIELD_PREP(PANIC0_THRES_HIGH_MASK, 2 * PANIC0_THRES_MAX / 3), > > > + writel(FIELD_PREP(PANIC0_THRES_LOW_MASK, DIV_ROUND_UP(1 * > > > PANIC0_THRES_MAX, 3)) | > > > + FIELD_PREP(PANIC0_THRES_HIGH_MASK, DIV_ROUND_UP(2 * > > > PANIC0_THRES_MAX, 3)), > > > > I am starting to wonder, whether this should be configurable in DT, because > > it seems there might be users that need to tweak the watermarks one way or > > the other for different video outputs ? > > +1 to provide a override mechanism via DT.
If this is related to the output resolution, the DT is the last place you should deal with this. Maxime
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