linux-kernel - Re: [PATCH 5/8] fbdev: ssd1307fb: Add module parameter bitsperpixel.

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Date:	Tue, 10 Mar 2015 12:45:49 +0200
From:	Tomi Valkeinen <tomi.valkeinen@...com>
To:	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Thomas Niederprüm <niederp@...sik.uni-kl.de>
CC:	<linux-fbdev@...r.kernel.org>, <plagnioj@...osoft.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/8] fbdev: ssd1307fb: Add module parameter bitsperpixel.

On 14/02/15 17:54, Maxime Ripard wrote:
> On Sat, Feb 07, 2015 at 05:05:03PM +0100, Thomas Niederprüm wrote:
>> Am Sat, 7 Feb 2015 12:20:43 +0100
>> schrieb Maxime Ripard <maxime.ripard@...e-electrons.com>:
>>
>>> On Fri, Feb 06, 2015 at 11:28:11PM +0100, niederp@...sik.uni-kl.de
>>> wrote:
>>>> From: Thomas Niederprüm <niederp@...sik.uni-kl.de>
>>>>
>>>> This patch adds a module parameter 'bitsperpixel' to adjust the
>>>> colordepth of the framebuffer. All values >1 will result in memory
>>>> map of the requested color depth. However only the MSB of each
>>>> pixel will be sent to the device. The framebuffer identifies itself
>>>> as a grayscale display with the specified depth.
>>>
>>> I'm not sure this is the right thing to do.
>>>
>>> The bits per pixel for this display is rightfully defined, used and
>>> reported to the userspace, why would you want to change that?
>>
>> You are right of course. The display is 1bpp and it reports to be 1
>> bpp. The problem is that there is almost no userspace library that can
>> handle 1 bit framebuffers correctly. So it is nice if the framebuffer
>> (optionally) can expose itself as 8 bits per pixel grayscale to the
>> userspace program. As an example this allows to run DirectFB on the
>> framebuffer, which is not possible out of the box for 1bpp.
>>
>> Also note that if do not set the module parameter at load time
>> the framebuffer will be 1bpp. So you have to actively set that module
>> parameter to make the framebuffer pretend to be more than 1bpp.
>>
>> In any case I don't cling to that patch, I just thought it was a nice
>> feature.
> 
> I'd say that the right fix would be to patch DirectFB, instead of
> faking that in the kernel.
> 
> But again, that's probably Tomi's call, not mine.

Right, I'm not thrilled =). I don't think it's a good idea to lie to the
userspace (except when fixing regressions).

 Tomi



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