[RFC 3/6] drm: add SimpleDRM driver

[David Herrmann]

Hi

On Wed, Jun 26, 2013 at 10:58 PM, Stephen Warren <swarren at wwwdotorg.org> wrote:
> On 06/24/2013 04:27 PM, David Herrmann wrote:
>> The SimpleDRM driver binds to simple-framebuffer devices and provides a
>> DRM/KMS API. It provides only a single CRTC+encoder+connector combination
>> plus one initial mode.
>>
>> Userspace can create one dumb-buffer and attach it to the CRTC. Only if
>> the buffer is destroyed, a new buffer can be created. The buffer is
>> directly mapped into user-space, so we have only resources for a single
>> buffer. Otherwise, shadow buffers plus damage-request would be needed.
>
>> diff --git a/drivers/gpu/drm/simpledrm/Kconfig b/drivers/gpu/drm/simpledrm/Kconfig
>
>> +config DRM_SIMPLEDRM
>> +     tristate "Simple firmware framebuffer DRM driver"
>> +     depends on DRM && !FB_SIMPLE
>> +     help
>> +       SimpleDRM can run on all systems with pre-initialized graphics
>> +       hardware. It uses a framebuffer that was initialized during
>> +       firmware boot. No page-flipping, modesetting or other advanced
>> +       features are available. However, other DRM drivers can be loaded
>> +       later and take over from SimpleDRM if they provide real hardware
>> +       support.
>> +
>> +       SimpleDRM supports: "simple-framebuffer" DeviceTree objects, x86 VESA
>> +       BIOS Extensions (VBE), EFI framebuffers
>
> DT objects, yes. I'm not sure it's quite true to say it actually
> directly supports VBE or EFI FBs; it's more the code in patch 2/6 that
> supports those. I guess this is a bit nit-picky of a distinction though.

I initially intended to add support for "platform-framebuffer"
objects, too. This would make vesafb/... obsolete but I dropped that
idea for now. I will fix the Kconfig description.

>> diff --git a/drivers/gpu/drm/simpledrm/simpledrm_drv.c b/drivers/gpu/drm/simpledrm/simpledrm_drv.c
>
>> +static int parse_dt(struct platform_device *pdev,
>> +                 struct simplefb_platform_data *mode)
>
>> +     strlcpy(mode->format, format, sizeof(mode->format));
>
> Even here, I believe the DT data sticks around so just copying the
> pointer should be safe. It'd be worth validating that for sure though.

Yep, indeed, I fixed that.

Thanks!
David

> I didn't review the DRM stuff here since I'm not at all familiar with DRM.