Hi Laurent,
On 05/23/2011 09:00 PM, Laurent Pinchart wrote:
On Saturday 21 May 2011 00:33:02 Florian Tobias Schandinat wrote:
On 05/17/2011 10:07 PM, Laurent Pinchart wrote:
- Other solutions are possible, such as adding new ioctls. Those
solutions are more intrusive, and require larger changes to both
userspace and kernelspace code.
I'm against (ab)using the nonstd field (probably the only sane thing we can
do with it is declare it non-standard which interpretation is completely
dependent on the specific driver) or requiring previously unused fields to
have a special value so I'd like to suggest a different method:
I remembered an earlier discussion:
[ http://marc.info/?l=linux-fbdev&m=129896686208130&w=2 ]
On 03/01/2011 08:07 AM, Geert Uytterhoeven wrote:
> On Tue, Mar 1, 2011 at 04:13, Damian<dhobs...@igel.co.jp> wrote:
>> On 2011/02/24 15:05, Geert Uytterhoeven wrote:
>>> For YUV (do you mean YCbCr?), I'm inclined to suggest adding a new
>>> FB_VISUAL_*
>>> type instead, which indicates the fb_var_screeninfo.{red,green,blue}
>>> fields are
>>> YCbCr instead of RGB.
>>> Depending on the frame buffer organization, you also need new
>>> FB_TYPE_*/FB_AUX_*
>>> types.
>>
>> I just wanted to clarify here. Is your comment about these new flags
>> in specific reference to this patch or to Magnus' "going forward"
>> comment? It
>
> About new flags.
>
>> seems like the beginnings of a method to standardize YCbCr support in
>> fbdev across all platforms.
>> Also, do I understand correctly that FB_VISUAL_ would specify the
>> colorspace
>
> FB_VISUAL_* specifies how pixel values (which may be tuples) are mapped
> to colors on the screen, so to me it looks like the sensible way to set
> up YCbCr.
>
>> (RGB, YCbCr), FB_TYPE_* would be a format specifier (i.e. planar,
>> semiplanar, interleaved, etc)? I'm not really sure what you are
>> referring to with the FB_AUX_* however.
>
> Yep, FB_TYPE_* specifies how pixel values/tuples are laid out in frame
> buffer memory.
>
> FB_AUX_* is only used if a specific value of FB_TYPE_* needs an
> additional parameter (e.g. the interleave value for interleaved
> bitplanes).
Adding new standard values for these fb_fix_screeninfo fields would solve
the issue for framebuffers which only support a single format.
I've never liked changing fixed screen information :-) It would be consistent
with the API though.
Fixed does only mean that it can't be directly manipulated by applications. The
driver has to modify it anyway on about every mode change (line_length). Yes
perhaps some of these fields would be in var today and certainly others
shouldn't exist at all but I do not blame anyone for not being capable to look
into the future.
If you have the need to switch
Yes I need that. This requires an API to set the mode through
fb_var_screeninfo, which is why I skipped modifying fb_fix_screeinfo.
A new FB_TYPE_* could be used to report that we use a 4CC-based mode, with the
exact mode reported in one of the fb_fix_screeninfo reserved fields (or the
type_aux field). This would duplicate the information passed through
fb_var_screeninfo though. Do you think it's worth it ?
I think it's more like a FB_VISUAL_FOURCC as you want to express how the color
<-> pixel mapping is. The FB_TYPE_* is more about whether pixel are packed or
represented as planes (the 2 format groups mentioned on fourcc.org).
That's certainly something I'd introduce as it would (hopefully) work to prevent
old applications which don't know your extension manipulating a FOURCC format
thinking that it is RGB.
So I think we should
fix.visual = FB_VISUAL_FOURCC;
fix.type = FB_TYPE_PACKED_PIXELS | FB_TYPE_PLANES; /* (?) */
or maybe add a FB_TYPE_FOURCC and rely only on the information in FOURCC (as
things like UYVY could become confusing as macropixel!=pixel)
I guess it would be a good idea to add a new flag to the vmode bitfield in
fb_var_screeninfo which looks like a general purpose modifier for the
videomode. You could than reuse any RGB-specific field you like to pass more
information.
That looks good to me. The grayscale field could be reused to pass the 4CC.
var.grayscale = <FOURCC_FORMAT>;
var.vmode = FB_VMODE_FOURCC;
and if this vmode flag is not set it means traditional mode (based on RGBA).
Maybe we should also use this chance to declare one of the fix_screeninfo
reserved fields to be used for capability flags or an API version as we can
assume that those are 0 (at least in sane drivers).
That's always good, although it's not a hard requirement for the purpose of
YUV support.
Sure. But it's good to let the application know whether you support the new
extension or whether you just ignore the flag. So I'm voting for a
fix.caps = FB_CAP_FOURCC;
Best regards,
Florian Tobias Schandinat
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