Re: [PATCH v2 0/2] Fixes for omapdrm console

Hi

Am 27.02.24 um 09:01 schrieb Tony Lindgren:

* Thomas Zimmermann [off-list ref] [240227 07:56]:

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Am 27.02.24 um 08:06 schrieb Tony Lindgren:

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* Tony Lindgren [off-list ref] [240226 13:26]:

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* Thomas Zimmermann [off-list ref] [240226 09:10]:

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Am 26.02.24 um 10:01 schrieb Tomi Valkeinen:

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On 26/02/2024 10:26, Tomi Valkeinen wrote:

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How is it broken? I don't usually use the console (or fbdev) but
enabling it now, it seems to work fine for me, on DRA76 EVM with
HDMI output.

Omapdrm implements drm_framebuffer_funcs.dirty withomap_framebuffer_dirty().
AFAIK DRM semantics requires to run the dirty helper after writing to the
framebuffer's memory. Userspace does this via the DIRTYFB ioctl. [1] But (at
least) for correctness the console needs to do the same.

[1] https://elixir.bootlin.com/linux/v6.7.6/source/drivers/gpu/drm/drm_ioctl.c#L679

Yes I noticed console not updating and bisected it down to the two
commits listed. I did the bisect on a droid4 though with command mode
LCD. I did not test with HDMI, will give that a try too.

I can reproduce the cache issue with Tomi's omapfb-tests [2] below:

while true;
        do dd if=/dev/urandom of=/dev/fb0
        ~/src/omapfb-tests/test
        sleep 1
done

That produces short random data stripes on the test image.

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After applying your patches, I see a lot of cache-related artifacts on
the screen when updating the fb.

I guess we might need a dma-specific mmap helper to make this work
correctly.

Comparing the difference between drm_gem_mmap_obj() and
fb_deferred_io_mmap(), the following test patch makes the cache issue
go away for me. Not sure if this can be set based on some flag, or if
we need a separate fb_deferred_io_wc_mmap() or something like that?

[2] https://github.com/tomba/omapfb-tests

8< --------------------

diff --git a/drivers/video/fbdev/core/fb_defio.c b/drivers/video/fbdev/core/fb_defio.c
--- a/drivers/video/fbdev/core/fb_defio.c
+++ b/drivers/video/fbdev/core/fb_defio.c

@@ -224,6 +224,7 @@ static const struct address_space_operations fb_deferred_io_aops = {
   int fb_deferred_io_mmap(struct fb_info *info, struct vm_area_struct *vma)
   {
   	vma->vm_page_prot = pgprot_decrypted(vma->vm_page_prot);
+	vma->vm_page_prot = pgprot_writecombine(vm_get_page_prot(vma->vm_flags));

Great, that's exactly what I had in mind!

OK :)

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My proposal is to add this mmap function directly to omapdrm. I'll later
take care of integrating this into the overall framework. I have a few other
ideas in mind that are related to this issue. Ok?

OK that sounds good to me, I'll post v3 set of patches.

I just realized the fb_deferred_io_mmap() is already exported. So please 
use it instead of duplicating the code in omapdrm.

[1] 
https://elixir.bootlin.com/linux/v6.7/source/drivers/video/fbdev/core/fb_defio.c#L237

I also noticed that omapdrm does not yet select the correct Kconfig 
symbols. That can be fixed by

  1) creating Kconfig FB_DMAMEM_HELPERS_DEFERRED that are similar to 
their SYSMEM equivalent at [2]. The tokens should look like this

configFB_DMAMEM_HELPERS_DEFERRED  <https://elixir.bootlin.com/linux/latest/K/ident/CONFIG_FB_SYSMEM_HELPERS_DEFERRED>
bool
depends onFB_CORE  <https://elixir.bootlin.com/linux/latest/K/ident/CONFIG_FB_CORE>
selectFB_DEFERRED_IO  <https://elixir.bootlin.com/linux/latest/K/ident/CONFIG_FB_DEFERRED_IO>
selectFB_DMAMEM_HELPERS  <https://elixir.bootlin.com/linux/latest/K/ident/CONFIG_FB_SYSMEM_HELPERS>


   2) and selecting it instead of FB_DMAMEM_HELPERS under omapdrm's 
Kconfig symbol.

[2] 
https://elixir.bootlin.com/linux/latest/source/drivers/video/fbdev/core/Kconfig#L147

Best regards
Thomas

Regards,

Tony

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)