# Re: \[PATCH 1/8\] fbdev/smscufx: Use fb\_ops helpers for deferred I/O

- From: Thomas Zimmermann \<tzimmermann@suse.de\>
- Date: 2023-09-04 14:39:54 
- List: linux-fbdev
- Page: https://ratatoskr.run/linux-fbdev/2023/09/8935629
- Thread: https://ratatoskr.run/linux-fbdev/2023/08/8935599/t.md

```text
Hi Javier

Am 04.09.23 um 14:59 schrieb Javier Martinez Canillas:
> Thomas Zimmermann [ref] writes:
>
> Hello Thomas,
>
>> Generate callback functions for struct fb_ops with the fbdev macro
>> FB_GEN_DEFAULT_DEFERRED_SYSMEM_OPS(). Initialize struct fb_ops to
>> the generated functions with fbdev initializer macros.
>>
>> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
>> Cc: Steve Glendinning <steve.glendinning@shawell.net>
>> ---
>
> The patch looks good to me, but I've a question below.
>
> Acked-by: Javier Martinez Canillas <javierm@redhat.com>
>
>>   drivers/video/fbdev/smscufx.c | 85 +++++++++--------------------------
>>   1 file changed, 22 insertions(+), 63 deletions(-)
>>
>> diff --git a/drivers/video/fbdev/smscufx.c b/drivers/video/fbdev/smscufx.c
>
> [...]
>
>>   static const struct fb_ops ufx_ops = {
>>   	.owner = THIS_MODULE,
>> -	.fb_read = fb_sys_read,
>> -	.fb_write = ufx_ops_write,
>> +	__FB_DEFAULT_DEFERRED_OPS_RDWR(ufx_ops),
>>   	.fb_setcolreg = ufx_ops_setcolreg,
>> -	.fb_fillrect = ufx_ops_fillrect,
>> -	.fb_copyarea = ufx_ops_copyarea,
>> -	.fb_imageblit = ufx_ops_imageblit,
>> +	__FB_DEFAULT_DEFERRED_OPS_DRAW(ufx_ops),
>>   	.fb_mmap = ufx_ops_mmap,
>
> There are no generated functions for .fb_mmap, I wonder what's the value
> of __FB_DEFAULT_DEFERRED_OPS_MMAP() ? Maybe just removing that macro and
> setting .fb_mmap = fb_deferred_io_mmap instead if there's no custom mmap
> handler would be easier to read ?

At least two drivers could use __FB_DEFAULT_DEFERRED_OPS_MMAP: picolcd-fb and hyperv_fb. At some point, we might want to set/clear fb_mmap depending on some Kconfig value. Having __FB_DEFAULT_DEFERRED_OPS_MMAP might be helpful then.

>
> Alternatively, __FB_DEFAULT_DEFERRED_OPS_MMAP() could still be left but
> not taking a __prefix argument since that is not used anyways ?

The driver optionally provides mmap without deferred I/O, hence the mmap function. That makes no sense, as these writes to the buffer would never make it to the device memory. But I didn't want to remove the code either. So I just left the existing function as-is. Usually, the deferred-I/O mmap is called immediately. [1]

Best regards
Thomas

[1] https://elixir.bootlin.com/linux/v6.5.1/source/drivers/video/fbdev/smscufx.c#L784

>

-- 
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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