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From:   Alistair Francis <alistair23@gmail.com>
Date:   Thu, 19 Aug 2021 18:16:00 +1000
Message-ID: <CAKmqyKNzojeRtYUZyfVDBhAz5gNfRendSWduYJV_+gYiz8QAMg@mail.gmail.com>
Subject: Re: Revert "video: fbdev: mxsfb: Remove driver"
To:     Sam Ravnborg <sam@ravnborg.org>
Cc:     Marek Vasut <marex@denx.de>, Fabio Estevam <festevam@gmail.com>,
        Shawn Guo <shawnguo@kernel.org>,
        Sascha Hauer <kernel@pengutronix.de>,
        dl-linux-imx <linux-imx@nxp.com>, b.zolnierkie@samsung.com,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Alistair Francis <alistair@alistair23.me>
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On Thu, Aug 19, 2021 at 4:31 AM Sam Ravnborg <sam@ravnborg.org> wrote:
>
> Hi Alistair,
>
> > 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?
>
> Just to try to verify this could you try to return early
> in the switch where we have FBIOPUT_VSCREENINFO?
>
> In fbmem.c in do_fb_ioctl() just add a printk("something\n") and
> return 0 in the FBIOPUT_VSCREENINFO case.

Yep, this diff changes the working screen with the fbdev driver to not working:

diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
index 1c855145711b..0f781914eca0 100644
--- a/drivers/video/fbdev/core/fbmem.c
+++ b/drivers/video/fbdev/core/fbmem.c
@@ -1099,18 +1099,8 @@ static long do_fb_ioctl(struct fb_info *info,
unsigned int cmd,
                ret = copy_to_user(argp, &var, sizeof(var)) ? -EFAULT : 0;
                break;
        case FBIOPUT_VSCREENINFO:
-               if (copy_from_user(&var, argp, sizeof(var)))
-                       return -EFAULT;
-               console_lock();
-               lock_fb_info(info);
-               ret = fb_set_var(info, &var);
-               if (!ret)
-                       fbcon_update_vcs(info, var.activate & FB_ACTIVATE_ALL);
-               unlock_fb_info(info);
-               console_unlock();
-               if (!ret && copy_to_user(argp, &var, sizeof(var)))
-                       ret = -EFAULT;
-               break;
+               printk("FBIOPUT_VSCREENINFO Returning early");
+               return -EINVAL;
        case FBIOGET_FSCREENINFO:
                lock_fb_info(info);
                memcpy(&fix, &info->fix, sizeof(fix));

So FBIOPUT_VSCREENINFO is the issue (or at least one of them).

Alistair

>
> The printk is just so something pops up in the logging.
>
> If this makes you going then we need to look at how to add this to the
> emulation or some other way to deal with this.
>
>         Sam