Re: [PATCH 04/10] drm/tegra: Set fbdev flags

Thomas Zimmermann
2023-07-05T09:20:30Z

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Hi Javier

Am 05.07.23 um 10:34 schrieb Javier Martinez Canillas:
> Thomas Zimmermann <tzimmermann@suse.de> writes:
>
>> Set fbdev default flags FBNFO_DEFAULT and mark the framebuffer with
>> FBINFO_VIRTFB. The framebuffer range is in DMA-able memory and should
>> be accessed with the CPU's regular memory ops.
>>
>> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
>> Cc: Thierry Reding <thierry.reding@gmail.com>
>> Cc: Mikko Perttunen <mperttunen@nvidia.com>
>> ---
>> drivers/gpu/drm/tegra/fbdev.c | 3 +++
>> 1 file changed, 3 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/tegra/fbdev.c b/drivers/gpu/drm/tegra/fbdev.c
>> index 82577b7c88da..8074430c52f1 100644
>> --- a/drivers/gpu/drm/tegra/fbdev.c
>> +++ b/drivers/gpu/drm/tegra/fbdev.c
>> @@ -103,6 +103,8 @@ static int tegra_fbdev_probe(struct drm_fb_helper *helper,
>> return PTR_ERR(info);
>> }
>>
>> + info->flags = FBINFO_DEFAULT;
>> +
>> fb = tegra_fb_alloc(drm, &cmd, &bo, 1);
>> if (IS_ERR(fb)) {
>> err = PTR_ERR(fb);
>> @@ -132,6 +134,7 @@ static int tegra_fbdev_probe(struct drm_fb_helper *helper,
>> }
>> }
>>
>> + info->flags |= FBINFO_VIRTFB;
>
> I see that all fbdev drivers just do: info->flags = FBINFO_FLAG_DEFAULT | FBINFO_VIRTFB
>
> Guess you are doing in two assignments to be consistent with drm_fbdev_dma.c ?
> I was just curious about the rationale for setting the flags in two steps.

The _DEFAULT flag is really just a zero. And the other flags describe
different aspects of the framebuffer. I think it makes sense to set the
flags together with the respective state. For example, _VIRTFB is set
next to ->screen_buffer, because they belong together.

_VIRTFB is currently only used in defio code at

https://elixir.bootlin.com/linux/latest/source/drivers/video/fbdev/core/fb_defio.c#L232

I think the fbdev I/O helpers should also test this flag after all
drivers have been annotated correctly. For example, fb_io_read() would
WARN_ONCE if the _VIRTFB flag has been set; and fb_sys_read() would warn
if it hasn't been set. For the read helpers, it also makes sense to
WARN_ONCE if the _READS_FAST flag has not been set.

Best regards
Thomas

>
> Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
>

--
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)

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