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");