Re: [PATCH 1/8] fbdev/smscufx: Use fb_ops helpers for deferred I/O

Thomas Zimmermann [off-list ref] writes:

Hi Javier

Am 04.09.23 um 14:59 schrieb Javier Martinez Canillas:

quoted

Thomas Zimmermann [off-list ref] writes:

Hello Thomas,

quoted

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>

quoted

  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

[...]

quoted

  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.

Got it, thanks for the explanation.

quoted

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]

Makes sense.

-- 
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat