Re: [PATCH v3 02/25] drm/dumb-buffers: Provide helper to set pitch and size

[Thomas Zimmermann <tzimmermann@xxxxxxx>]

Hi

Am 20.02.25 um 10:18 schrieb Tomi Valkeinen:
[...]
> > + * Color modes of 10, 12, 15, 30 and 64 are only supported for use by
> > + * legacy user space. Please don't use them in new code. Other modes
> > + * are not support.
> > + *
> > + * Do not attempt to allocate anything but linear framebuffer memory
> > + * with single-plane RGB data. Allocation of other framebuffer
> > + * layouts requires dedicated ioctls in the respective DRM driver.
> According to this, every driver that supports, say, NV12, should 
> implement their own custom ioctl to do the exact same thing? And, of 
> course, every userspace app that uses, say, NV12, should then add code 
> for all these platforms to call the custom ioctls?
Yes, that's exactly the current status.

There has been discussion about a new dumb-create ioctl that takes a DRM 
format as parameter. I'm all for it, but it's out of the scope for this 
series.
> As libdrm's modetest currently supports YUV formats with dumb buffers, 
> should we remove that code, as it's not correct and I'm sure people 
> use libdrm code as a reference?
Of course not.

> Well, I'm not serious above, but I think all my points from the 
> earlier version are still valid. I don't like this. It changes the 
> parameters of the ioctl (bpp used to be bits-per-pixel, not it's 
> "color mode"), and the behavior of the ioctl, behavior that we've had 
> for a very long time, and we have no idea how many users there are 
> that will break (could be none, of course). And the documentation 
> changes make the current behavior and uses wrong or legacy.
Before I go into details about this statement, what use case exactly are 
you referring to when you say that behavior changes?
Best regards
Thomas

> Clearly we need something new and better for the buffer allocation, 
> but for the time being, I'd be more comfortable just keep the current 
> behavior, at least for all the drivers I use or maintain: omapdrm, 
> tidss, renesas, xlnx, tilcdc.
>  Tomi
--
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Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
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