Re: [PATCH v4 13/13] drm/i915: Implement dedicated fbdev I/O helpers

[Sui Jingfeng <15330273260@xxxxxx>]

Hi,

On 2023/5/30 03:36, Sam Ravnborg wrote:
> Hi Thomas,
>
> On Wed, May 24, 2023 at 11:21:50AM +0200, Thomas Zimmermann wrote:
> > Implement dedicated fbdev helpers for framebuffer I/O instead
> > of using DRM's helpers. Use an fbdev generator macro for
> > deferred I/O to create the fbdev callbacks. i915 was the only
> > caller of the DRM helpers, so remove them from the helper module.
> >
> > i915's fbdev emulation is still incomplete as it doesn't implement
> > deferred I/O and damage handling for mmaped pages.
> >
> > v4:
> > 	* generate deferred-I/O helpers
> > 	* use initializer macros for fb_ops
> > v2:
> > 	* use FB_IO_HELPERS options
> >
> > Signed-off-by: Thomas Zimmermann <tzimmermann@xxxxxxx>
> > Cc: Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx>
> > Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
> > Cc: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
> > Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx>
> > Cc: "Ville Syrjälä" <ville.syrjala@xxxxxxxxxxxxxxx>
> > ---
> >   drivers/gpu/drm/Kconfig                    |   3 -
> >   drivers/gpu/drm/drm_fb_helper.c            | 107 ---------------------
> >   drivers/gpu/drm/i915/Kconfig               |   1 +
> >   drivers/gpu/drm/i915/display/intel_fbdev.c |  14 +--
> >   include/drm/drm_fb_helper.h                |  39 --------
> >   5 files changed, 9 insertions(+), 155 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> > index 92a782827b7b..bb2e48cc6cd6 100644
> > --- a/drivers/gpu/drm/Kconfig
> > +++ b/drivers/gpu/drm/Kconfig
> > @@ -133,9 +133,6 @@ config DRM_FBDEV_EMULATION
> >   	bool "Enable legacy fbdev support for your modesetting driver"
> >   	depends on DRM_KMS_HELPER
> >   	depends on FB=y || FB=DRM_KMS_HELPER
> > -	select FB_CFB_FILLRECT
> > -	select FB_CFB_COPYAREA
> > -	select FB_CFB_IMAGEBLIT
> >   	select FRAMEBUFFER_CONSOLE if !EXPERT
> >   	select FRAMEBUFFER_CONSOLE_DETECT_PRIMARY if FRAMEBUFFER_CONSOLE
> >   	default y
> > diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> > index bab6b252f02a..9978147bbc8a 100644
> > --- a/drivers/gpu/drm/drm_fb_helper.c
> > +++ b/drivers/gpu/drm/drm_fb_helper.c
> > @@ -736,113 +736,6 @@ void drm_fb_helper_deferred_io(struct fb_info *info, struct list_head *pagerefli
> >   }
> >   EXPORT_SYMBOL(drm_fb_helper_deferred_io);
> >   
> > -/**
> > - * drm_fb_helper_cfb_read - Implements struct &fb_ops.fb_read for I/O memory
> > - * @info: fb_info struct pointer
> > - * @buf: userspace buffer to read from framebuffer memory
> > - * @count: number of bytes to read from framebuffer memory
> > - * @ppos: read offset within framebuffer memory
> > - *
> > - * Returns:
> > - * The number of bytes read on success, or an error code otherwise.
> > - */
> > -ssize_t drm_fb_helper_cfb_read(struct fb_info *info, char __user *buf,
> > -			       size_t count, loff_t *ppos)
> > -{
> > -	return fb_io_read(info, buf, count, ppos);
> > -}
> > -EXPORT_SYMBOL(drm_fb_helper_cfb_read);
> > -
> > -/**
> > - * drm_fb_helper_cfb_write - Implements struct &fb_ops.fb_write for I/O memory
> > - * @info: fb_info struct pointer
> > - * @buf: userspace buffer to write to framebuffer memory
> > - * @count: number of bytes to write to framebuffer memory
> > - * @ppos: write offset within framebuffer memory
> > - *
> > - * Returns:
> > - * The number of bytes written on success, or an error code otherwise.
> > - */
> > -ssize_t drm_fb_helper_cfb_write(struct fb_info *info, const char __user *buf,
> > -				size_t count, loff_t *ppos)
> > -{
> > -	struct drm_fb_helper *helper = info->par;
> > -	loff_t pos = *ppos;
> > -	ssize_t ret;
> > -	struct drm_rect damage_area;
> > -
> > -	ret = fb_io_write(info, buf, count, ppos);
> > -	if (ret <= 0)
> > -		return ret;
> > -
> > -	if (helper->funcs->fb_dirty) {
> > -		drm_fb_helper_memory_range_to_clip(info, pos, ret, &damage_area);
> > -		drm_fb_helper_damage(helper, damage_area.x1, damage_area.y1,
> > -				     drm_rect_width(&damage_area),
> > -				     drm_rect_height(&damage_area));
> > -	}
> The generated helpers do not have the if (helper->funcs->fb_dirty)
> check.

Nice catch!

If I understand this correctly, fb_io_write() will write directly to the 
ultimate

destination. There no need to check if (helper->funcs->fb_dirty) anymore.

code inside the curly brace of  `if (helper->funcs->fb_dirty) { }`  can 
be delete safely .


This could turn out to be an optimization. This is a benefit of 
untangled implement.

previously this is a generic (tangled) implement, which intended to be 
used by both

the UMA device driver and non-UMA device(with dedicate VRAM) driver.


drm_fbdev_generic always has a shadow screen buffer allocated in system RAM,

 it always has the fb_dirty hooked, so this could be an optimization 
for fbdev_generic

by eliminate if (helper->funcs->fb_dirty) check.


while dma helper based driver could switch to drm_fbdev_dma, they writing

to gem buffer directly, no shadow buffer is needed.


With those patch, device driver with dedicated video memory can also 
choose FB_CFB_*

to update (iomem)framebuffer directly, despite slower.


> Is this implemented somewhere else that I missed?
>
> 	Sam
drm_fb_helper_fb_dirty() function has a check:

```

    if (drm_WARN_ON_ONCE(dev, !helper->funcs->fb_dirty))
        return;
```

Not sure if this is a little bit too late......

> > -
> > -	return ret;
> > -}
> > -EXPORT_SYMBOL(drm_fb_helper_cfb_write);
> > -
> > -/**
> > - * drm_fb_helper_cfb_fillrect - wrapper around cfb_fillrect
> > - * @info: fbdev registered by the helper
> > - * @rect: info about rectangle to fill
> > - *
> > - * A wrapper around cfb_fillrect implemented by fbdev core
> > - */
> > -void drm_fb_helper_cfb_fillrect(struct fb_info *info,
> > -				const struct fb_fillrect *rect)
> > -{
> > -	struct drm_fb_helper *helper = info->par;
> > -
> > -	cfb_fillrect(info, rect);
> > -
> > -	if (helper->funcs->fb_dirty)
> > -		drm_fb_helper_damage(helper, rect->dx, rect->dy, rect->width, rect->height);
> > -}
> > -EXPORT_SYMBOL(drm_fb_helper_cfb_fillrect);
> > -
> > -/**
> > - * drm_fb_helper_cfb_copyarea - wrapper around cfb_copyarea
> > - * @info: fbdev registered by the helper
> > - * @area: info about area to copy
> > - *
> > - * A wrapper around cfb_copyarea implemented by fbdev core
> > - */
> > -void drm_fb_helper_cfb_copyarea(struct fb_info *info,
> > -				const struct fb_copyarea *area)
> > -{
> > -	struct drm_fb_helper *helper = info->par;
> > -
> > -	cfb_copyarea(info, area);
> > -
> > -	if (helper->funcs->fb_dirty)
> > -		drm_fb_helper_damage(helper, area->dx, area->dy, area->width, area->height);
> > -}
> > -EXPORT_SYMBOL(drm_fb_helper_cfb_copyarea);
> > -
> > -/**
> > - * drm_fb_helper_cfb_imageblit - wrapper around cfb_imageblit
> > - * @info: fbdev registered by the helper
> > - * @image: info about image to blit
> > - *
> > - * A wrapper around cfb_imageblit implemented by fbdev core
> > - */
> > -void drm_fb_helper_cfb_imageblit(struct fb_info *info,
> > -				 const struct fb_image *image)
> > -{
> > -	struct drm_fb_helper *helper = info->par;
> > -
> > -	cfb_imageblit(info, image);
> > -
> > -	if (helper->funcs->fb_dirty)
> > -		drm_fb_helper_damage(helper, image->dx, image->dy, image->width, image->height);
> > -}
> > -EXPORT_SYMBOL(drm_fb_helper_cfb_imageblit);
> > -
> >   /**
> >    * drm_fb_helper_set_suspend - wrapper around fb_set_suspend
> >    * @fb_helper: driver-allocated fbdev helper, can be NULL
> > diff --git a/drivers/gpu/drm/i915/Kconfig b/drivers/gpu/drm/i915/Kconfig
> > index e4f4d2e3fdfe..01b5a8272a27 100644
> > --- a/drivers/gpu/drm/i915/Kconfig
> > +++ b/drivers/gpu/drm/i915/Kconfig
> > @@ -17,6 +17,7 @@ config DRM_I915
> >   	select DRM_KMS_HELPER
> >   	select DRM_PANEL
> >   	select DRM_MIPI_DSI
> > +	select FB_IO_HELPERS if DRM_FBDEV_EMULATION
> >   	select RELAY
> >   	select I2C
> >   	select I2C_ALGOBIT
> > diff --git a/drivers/gpu/drm/i915/display/intel_fbdev.c b/drivers/gpu/drm/i915/display/intel_fbdev.c
> > index aab1ae74a8f7..eccaceaf8b9d 100644
> > --- a/drivers/gpu/drm/i915/display/intel_fbdev.c
> > +++ b/drivers/gpu/drm/i915/display/intel_fbdev.c
> > @@ -28,6 +28,7 @@
> >   #include <linux/console.h>
> >   #include <linux/delay.h>
> >   #include <linux/errno.h>
> > +#include <linux/fb.h>
> >   #include <linux/init.h>
> >   #include <linux/kernel.h>
> >   #include <linux/mm.h>
> > @@ -84,6 +85,10 @@ static void intel_fbdev_invalidate(struct intel_fbdev *ifbdev)
> >   	intel_frontbuffer_invalidate(to_frontbuffer(ifbdev), ORIGIN_CPU);
> >   }
> >   
> > +FB_GEN_DEFAULT_DEFERRED_IO_OPS(intel_fbdev,
> > +			       drm_fb_helper_damage_range,
> > +			       drm_fb_helper_damage_area)
> > +
> >   static int intel_fbdev_set_par(struct fb_info *info)
> >   {
> >   	struct intel_fbdev *ifbdev = to_intel_fbdev(info->par);
> > @@ -132,15 +137,12 @@ static int intel_fbdev_mmap(struct fb_info *info, struct vm_area_struct *vma)
> >   
> >   static const struct fb_ops intelfb_ops = {
> >   	.owner = THIS_MODULE,
> > +	__FB_DEFAULT_DEFERRED_OPS_RDWR(intel_fbdev),
> >   	DRM_FB_HELPER_DEFAULT_OPS,
> >   	.fb_set_par = intel_fbdev_set_par,
> > -	.fb_read = drm_fb_helper_cfb_read,
> > -	.fb_write = drm_fb_helper_cfb_write,
> > -	.fb_fillrect = drm_fb_helper_cfb_fillrect,
> > -	.fb_copyarea = drm_fb_helper_cfb_copyarea,
> > -	.fb_imageblit = drm_fb_helper_cfb_imageblit,
> > -	.fb_pan_display = intel_fbdev_pan_display,
> >   	.fb_blank = intel_fbdev_blank,
> > +	.fb_pan_display = intel_fbdev_pan_display,
> > +	__FB_DEFAULT_DEFERRED_OPS_DRAW(intel_fbdev),
> >   	.fb_mmap = intel_fbdev_mmap,
> >   };
> >   
> > diff --git a/include/drm/drm_fb_helper.h b/include/drm/drm_fb_helper.h
> > index b50fd0c0b713..4863b0f8299e 100644
> > --- a/include/drm/drm_fb_helper.h
> > +++ b/include/drm/drm_fb_helper.h
> > @@ -258,18 +258,6 @@ void drm_fb_helper_damage_area(struct fb_info *info, u32 x, u32 y, u32 width, u3
> >   
> >   void drm_fb_helper_deferred_io(struct fb_info *info, struct list_head *pagereflist);
> >   
> > -ssize_t drm_fb_helper_cfb_read(struct fb_info *info, char __user *buf,
> > -			       size_t count, loff_t *ppos);
> > -ssize_t drm_fb_helper_cfb_write(struct fb_info *info, const char __user *buf,
> > -				size_t count, loff_t *ppos);
> > -
> > -void drm_fb_helper_cfb_fillrect(struct fb_info *info,
> > -				const struct fb_fillrect *rect);
> > -void drm_fb_helper_cfb_copyarea(struct fb_info *info,
> > -				const struct fb_copyarea *area);
> > -void drm_fb_helper_cfb_imageblit(struct fb_info *info,
> > -				 const struct fb_image *image);
> > -
> >   void drm_fb_helper_set_suspend(struct drm_fb_helper *fb_helper, bool suspend);
> >   void drm_fb_helper_set_suspend_unlocked(struct drm_fb_helper *fb_helper,
> >   					bool suspend);
> > @@ -385,33 +373,6 @@ static inline int drm_fb_helper_defio_init(struct drm_fb_helper *fb_helper)
> >   	return -ENODEV;
> >   }
> >   
> > -static inline ssize_t drm_fb_helper_cfb_read(struct fb_info *info, char __user *buf,
> > -					     size_t count, loff_t *ppos)
> > -{
> > -	return -ENODEV;
> > -}
> > -
> > -static inline ssize_t drm_fb_helper_cfb_write(struct fb_info *info, const char __user *buf,
> > -					      size_t count, loff_t *ppos)
> > -{
> > -	return -ENODEV;
> > -}
> > -
> > -static inline void drm_fb_helper_cfb_fillrect(struct fb_info *info,
> > -					      const struct fb_fillrect *rect)
> > -{
> > -}
> > -
> > -static inline void drm_fb_helper_cfb_copyarea(struct fb_info *info,
> > -					      const struct fb_copyarea *area)
> > -{
> > -}
> > -
> > -static inline void drm_fb_helper_cfb_imageblit(struct fb_info *info,
> > -					       const struct fb_image *image)
> > -{
> > -}
> > -
> >   static inline void drm_fb_helper_set_suspend(struct drm_fb_helper *fb_helper,
> >   					     bool suspend)
> >   {
> > --
> > 2.40.1
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel