linux-kernel - Re: [RFC 0/6] SimpleDRM Driver (was: dvbe driver)

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Date:	Wed, 26 Jun 2013 15:30:15 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	David Herrmann <dh.herrmann@...il.com>
CC:	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	Dave Airlie <airlied@...il.com>, linux-fbdev@...r.kernel.org,
	Stephen Warren <swarren@...dia.com>,
	Olof Johansson <olof@...om.net>
Subject: Re: [RFC 0/6] SimpleDRM Driver (was: dvbe driver)

On 06/24/2013 04:27 PM, David Herrmann wrote:
> Hi
> 
> This is my second revision of the dvbe driver. I renamed it to SimpleDRM to
> show the resemblence with the recently introduced simplefb.c fbdev driver. The
> driver is supposed to be the most basic DRM driver similar to efifb.c, vesafb.c,
> offb.c, simplefb.c, ...
> It provides a single virtual CRTC+encoder+connector and allows user-space to
> create one dumb-buffer at a time and attach it.
> 
> The setup changed slightly. It no longer uses shadow buffers but instead maps
> the framebuffer directly into userspace. Furthermore, a new infrastructure is
> used to unload firmware drivers during real hardware drivers probe cycles. Only
> nouveau was changed to use it, yet.
> 
> I still have an odd problem when unloading DRM drivers (not just SimpleDRM) with
> an fbdev fallback. If I call printk() directly after unregister_framebufer(), I
> get a NULL-deref somewhere in the VT layer (most times hide_cursor()). I haven't
> figured out exactly where that happens, but I am also very reluctant to spend
> more time debugging the VT layer.

I tested this on a Tegra ARM system, and it basically worked.

I have one question: With the simplefb driver, and console=tty1 on the
kernel command-line, I see both the penguins logo and Linux's boot
messages on the LCD panel that's hooked up through simplefb. However,
with simpledrm, I only see the penguins logo, but no boot messages. Is
that expected? How would I solve that if so?

Note: I needed to apply the following patch to get it to compile:

diff --git a/drivers/gpu/drm/simpledrm/simpledrm_fbdev.c
b/drivers/gpu/drm/simpledrm/simpledrm_fbdev.c
index 40a2696..39885c8 100644
--- a/drivers/gpu/drm/simpledrm/simpledrm_fbdev.c
+++ b/drivers/gpu/drm/simpledrm/simpledrm_fbdev.c
@@ -159,7 +159,7 @@ void sdrm_fbdev_cleanup(struct sdrm_device *sdrm)
 {
        struct fb_info *info;

-       if (!sdrm->info)
+       if (!sdrm->fbdev)
                return;

        dev_info(sdrm->ddev->dev, "fbdev cleanup\n");



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