linux-kernel - Re: Revert "video: fbdev: mxsfb: Remove driver"

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Date:   Thu, 19 Aug 2021 19:10:00 +1000
From:   Alistair Francis <alistair23@...il.com>
To:     Sam Ravnborg <sam@...nborg.org>
Cc:     Marek Vasut <marex@...x.de>, Fabio Estevam <festevam@...il.com>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <kernel@...gutronix.de>,
        dl-linux-imx <linux-imx@....com>, b.zolnierkie@...sung.com,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Alistair Francis <alistair@...stair23.me>
Subject: Re: Revert "video: fbdev: mxsfb: Remove driver"

On Thu, Aug 19, 2021 at 4:38 AM Sam Ravnborg <sam@...nborg.org> wrote:
>
> Hi Alistair,
>
> >
> > These are the EINVAL strace tells me in the not working case:
> >
> > prctl(PR_CAPBSET_READ, 0x30 /* CAP_??? */) = -1 EINVAL (Invalid argument)
> > prctl(PR_CAPBSET_READ, 0x2c /* CAP_??? */) = -1 EINVAL (Invalid argument)
> > prctl(PR_CAPBSET_READ, 0x2a /* CAP_??? */) = -1 EINVAL (Invalid argument)
> > prctl(PR_CAPBSET_READ, 0x29 /* CAP_??? */) = -1 EINVAL (Invalid argument)
> > ioctl(5, FBIOPUT_VSCREENINFO, 0x4ce8e0) = -1 EINVAL (Invalid argument)
> >
> > I'm guessing it's related to FBIOPUT_VSCREENINFO then, is that
> > something that could be added to the DRM emulation?
>
> If it turns out FBIOPUT_VSCREENINFO is the culprint it would also be
> good to know why we see EINVAL.
> One way is to sprinkle a number of printk's in fb_set_var(),
> then you can see how far you get before it fails.

Thanks for the help.

I see this line:

ret = info->fbops->fb_check_var(var, info);

in fb_set_var()

returning early.

Alistair

>
> This could hopefully give a clue why this fails with fbdev emulation.
>
>         Sam