linux-kernel - Re: [RFC 1/6] drm: Add top level Kconfig option for DRM fbdev emulation

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Date:	Tue, 10 Mar 2015 15:22:49 +0530
From:	Archit Taneja <architt@...eaurora.org>
To:	robdclark@...il.com, airlied@...ux.ie, treding@...dia.com,
	p.zabel@...gutronix.de, benjamin.gaignard@...aro.org,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	linux-arm-msm@...r.kernel.org, daniel@...ll.ch,
	daniel.vetter@...ll.ch
Subject: Re: [RFC 1/6] drm: Add top level Kconfig option for DRM fbdev emulation



On 03/10/2015 03:17 PM, Daniel Vetter wrote:
> On Tue, Mar 10, 2015 at 03:11:28PM +0530, Archit Taneja wrote:
>> Legacy fbdev emulation support via DRM is achieved through KMS FB helpers.
>> Most modesetting drivers enable provide fbdev emulation by default by selecting
>> KMS FB helpers. A few provide a separate Kconfig option for the user to enable
>> or disbale fbdev emulation.
>>
>> Enabling fbdev emulation is finally a distro-level decision. Having a top level
>> Kconfig option for fbdev emulation helps by providing a uniform way to
>> enable/disable fbdev emulation for any modesetting driver. It also lets us
>> remove unnecessary driver specific Kconfig options that causes bloat.
>>
>> With a top level Kconfig in place, we can stub out the fb helper functions when
>> not needed without breaking functionality. Having stub functions also prevents
>> drivers to require wrapping fb helper function calls with #ifdefs.
>>
>> DRM_FBDEV_EMULATION defaults to y since many drivers enable fbdev emulation by
>> default and majority of distributions expect the fbdev interface in the kernel.
>>
>> For now, this config selects both FB_SYS_* and FB_CFB_* configs as some
>> modesetting drivers use the former and other the later. This needs to be taken
>> care of in a better way.
>>
>> Signed-off-by: Archit Taneja <architt@...eaurora.org>
>> ---
>>   drivers/gpu/drm/Kconfig     |  18 +++++++
>>   drivers/gpu/drm/Makefile    |   4 ++
>>   include/drm/drm_fb_helper.h | 120 ++++++++++++++++++++++++++++++++++++++++++++
>>   3 files changed, 142 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
>> index 151a050..38f83a0 100644
>> --- a/drivers/gpu/drm/Kconfig
>> +++ b/drivers/gpu/drm/Kconfig
>> @@ -40,6 +40,24 @@ config DRM_KMS_FB_HELPER
>>   	help
>>   	  FBDEV helpers for KMS drivers.
>>
>> +config DRM_FBDEV_EMULATION
>> +	bool "Enable legacy fbdev support for your modesetting driver"
>> +	depends on DRM
>> +	select DRM_KMS_HELPER
>> +	select DRM_KMS_FB_HELPER
>> +	select FB_SYS_FILLRECT
>> +	select FB_SYS_COPYAREA
>> +	select FB_SYS_IMAGEBLIT
>> +	select FB_SYS_FOPS
>> +	select FB_CFB_FILLRECT
>> +	select FB_CFB_COPYAREA
>> +	select FB_CFB_IMAGEBLIT
>> +	default y
>> +	help
>> +	  Choose this option if you have a need for the legacy fbdev
>> +	  support. Note that this support also provide the linux console
>> +	  support on top of your modesetting driver.
>
> Maybe clarify that for linux console support you also need
> CONFIG_FRAMEBUFFER_CONSOLE? fbdev alone isn't enough.

DRM_KMS_FB_HELPER selects that for us, right?

Archit
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