Re: [PATCH] drm/fbdev-dma: fix getting smem_start

[Thomas Zimmermann]

Hi

Am 11.06.24 um 10:23 schrieb Peng Fan:
> > Subject: Re: [PATCH] drm/fbdev-dma: fix getting smem_start
> >
> > Hi
> >
> > Am 11.06.24 um 03:00 schrieb Peng Fan:
> > > > Subject: Re: [PATCH] drm/fbdev-dma: fix getting smem_start
> > > >
> > > > Hi
> > > >
> > > > Am 04.06.24 um 10:03 schrieb Peng Fan (OSS):
> > > > > From: Peng Fan <peng.fan@xxxxxxx>
> > > > >
> > > > > If 'info->screen_buffer' locates in vmalloc address space,
> > > > > virt_to_page will not be able to get correct results. With
> > > > > CONFIG_DEBUG_VM and CONFIG_DEBUG_VIRTUAL enabled on ARM64,
> > > > there is dump below:
> > > >
> > > > Which graphics driver triggers this bug?
> > > It is NXP i.MX95 DPU driver which is still in NXP downstream repo.
> > Which DRM memory manager does that driver use?
> DRM_GEM_DMA_DRIVER_OPS

So fbdev-dma would be correct. But with the gem-dma allocator, wouldn't 
you allocate from one of these dma_alloc_() calls at [1] ? How does the 
drivers end up with vmalloc'd fbdev memory? Specifically in the light of 
the docs at [2].

[1] 
https://elixir.bootlin.com/linux/v6.9/source/drivers/gpu/drm/drm_gem_dma_helper.c#L146
[2] 
https://elixir.bootlin.com/linux/v6.9/source/Documentation/core-api/dma-api-howto.rst#L124

Best regards
Thomas

> > I'm asking because if the driver allocates BOs via vmalloc(), should it really
> > use fbdev-dma?
> We use it for fbdev emulation. If drm_kms_helper.fbdev_emulation is 0,
> fbdev emulation could be disabled.
>
> Thanks
> Peng
> > Best regards
> > Thomas
> >
> > > Thanks,
> > > Peng.
> > --
> > --
> > 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)

--
--
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)