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From: Thomas Zimmermann <tzimmermann@suse.de>
To: Daniel Vetter <daniel@ffwll.ch>,
	Geert Uytterhoeven <geert@linux-m68k.org>
Cc: bluescreen_avenger@verizon.net, Jonathan Corbet <corbet@lwn.net>,
	David Airlie <airlied@linux.ie>,
	Emil Velikov <emil.l.velikov@gmail.com>,
	DRI Development <dri-devel@lists.freedesktop.org>,
	"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
	Liam Girdwood <lgirdwood@gmail.com>,
	virtualization@lists.linux-foundation.org,
	Hans de Goede <hdegoede@redhat.com>,
	Mark Brown <broonie@kernel.org>,
	Gerd Hoffmann <kraxel@redhat.com>,
	Greg KH <gregkh@linuxfoundation.org>,
	Sam Ravnborg <sam@ravnborg.org>
Subject: Re: [PATCH v4 0/9] drm: Support simple-framebuffer devices and firmware fbs
Date: Mon, 26 Apr 2021 14:18:05 +0200
Message-ID: <86308b36-57ec-a796-90c1-e4349e914823@suse.de> (raw)
In-Reply-To: <YH6U92Q71ntU6Z1R@phenom.ffwll.local>

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Hi

Am 20.04.21 um 10:46 schrieb Daniel Vetter:
> On Mon, Apr 19, 2021 at 10:00:56AM +0200, Geert Uytterhoeven wrote:
>> Hi Thomas,
>>
>> On Fri, Apr 16, 2021 at 11:00 AM Thomas Zimmermann <tzimmermann@suse.de> wrote:
>>> This patchset adds support for simple-framebuffer platform devices and
>>> a handover mechanism for native drivers to take-over control of the
>>> hardware.
>>>
>>> The new driver, called simpledrm, binds to a simple-frambuffer platform
>>> device. The kernel's boot code creates such devices for firmware-provided
>>> framebuffers, such as EFI-GOP or VESA. Typically the BIOS, UEFI or boot
>>> loader sets up the framebuffers. Description via device tree is also an
>>> option.
>>
>> I guess this can be used as a replacement for offb, too...
>>
>>> Patches 4 to 8 add the simpledrm driver. It's build on simple DRM helpers
>>> and SHMEM. It supports 16-bit, 24-bit and 32-bit RGB framebuffers. During
>>
>> .... if support for 8-bit frame buffers would be added?

Offb doesn't seem to be tied to the simple-framebuffer support. So 
adding a new driver or extending the simple-framebuffer code would be 
required. Not a big deal, though. Patch 3 of this patchset adds the 
ability to create generic drivers within DRM.

> 
> Is that 8-bit greyscale or 8-bit indexed with 256 entry palette? Former
> shouldn't be a big thing, but the latter is only really supported by the
> overall drm ecosystem in theory. Most userspace assumes that xrgb8888
> works, and we keep that illusion up by emulating it in kernel for hw which
> just doesn't support it. But reformatting xrgb8888 to c8 is tricky at
> best. The uapis are all there for setting the palette, and C8 is a defined
> format even with atomic kms interface, but really there's not much
> userspace for it. In other words, it would work as well as current offb
> would, but that's at least that.

I think we can just use a shadow palette in the drm driver: If the drm 
framebuffer is in C8, use the userspace's palette. If the drm 
framebuffer is in XRGB, use a palette that represents RGB332. The driver 
would do on-the-fly conversion; just like cirrus does.

Best regards
Thomas

> -Daniel
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer


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  parent reply index

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-16  9:00 Thomas Zimmermann
2021-04-16  9:00 ` [PATCH v4 1/9] drm/format-helper: Pass destination pitch to drm_fb_memcpy_dstclip() Thomas Zimmermann
2021-04-16  9:00 ` [PATCH v4 2/9] drm/format-helper: Add blitter functions Thomas Zimmermann
2021-04-16  9:00 ` [PATCH v4 3/9] drm/aperture: Add infrastructure for aperture ownership Thomas Zimmermann
2021-04-16  9:00 ` [PATCH v4 4/9] drm: Add simpledrm driver Thomas Zimmermann
2021-04-16  9:00 ` [PATCH v4 5/9] drm/simpledrm: Add fbdev emulation Thomas Zimmermann
2021-04-16  9:00 ` [PATCH v4 6/9] drm/simpledrm: Initialize framebuffer data from device-tree node Thomas Zimmermann
2021-04-16  9:00 ` [PATCH v4 7/9] drm/simpledrm: Acquire clocks from DT device node Thomas Zimmermann
2021-04-16  9:00 ` [PATCH v4 8/9] drm/simpledrm: Acquire regulators " Thomas Zimmermann
2021-04-16  9:00 ` [PATCH v4 9/9] drm/simpledrm: Acquire memory aperture for framebuffer Thomas Zimmermann
2021-04-19  8:00 ` [PATCH v4 0/9] drm: Support simple-framebuffer devices and firmware fbs Geert Uytterhoeven
2021-04-20  8:46   ` Daniel Vetter
2021-04-20  9:16     ` Geert Uytterhoeven
2021-04-20 11:11       ` Daniel Vetter
2021-04-20  9:22     ` Gerd Hoffmann
2021-04-20  9:27       ` Geert Uytterhoeven
2021-04-26 12:22         ` Thomas Zimmermann
2021-04-26 19:05           ` Geert Uytterhoeven
2021-04-26 12:18     ` Thomas Zimmermann [this message]
2021-04-26 15:08       ` Daniel Vetter
2021-04-29 10:24 ` Maxime Ripard

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