> Subject: i.MX8MP IMX-LCDIF Underrun Question(s)
>
> I have been testing various settings on the HDMI out of the i.MX8MP.
>
> I noticed that sometimes my monitor would not sync, but sometimes it
> would on the same resolution/refresh rate. Frieder noted the LCDIF
> was sometimes underflowing, so read up on it a little bit.
>
> In the comments of the LCDIF driver, it's noted:
> Set FIFO Panic watermarks, low 1/3, high 2/3 .
>
> However, in the downstream kernels, NXP changes the threshold to
> 1/2 and 3/4 on the LCDIF that drives the HDMI, while leaving the other
> LCDIF interfaces at the default.
>
> When I increased the threshold to 1/2 and 3/4, it appeared that several
> resolutions that my monitor was struggling to sync started working,
> and it appeared to sync faster. I don't have an HDMI analyzer, so I
> cannot verify much beyond knowing if my monitor can or cannot sync.
You mean the two?
thres-low = <1 2>; /* (FIFO * 1 / 2) */
thres-high = <3 4>; /* (FIFO * 3 / 4) */
>
> Could the threshold and underrun cause this monitor intermittent issue,
> or would this be something else?
The threshold could cause display flicker if the value could not satisfy
the bandwidth.
>
> Does it make sense to have a flag or device tree option to override the
> default thresholds to change the panic level?
I think it would be good to have a property as above.
+ DT maintainer to comment.
Regards
Peng.
>
> adam
