Re: [PATCH v3 6/7] drm/fb_helper: Support framebuffers in I/O memory

Daniel Vetter
2020-10-02T19:36:14Z

On Fri, Oct 2, 2020 at 8:05 PM Daniel Vetter <daniel@ffwll.ch> wrote:
>
> On Tue, Sep 29, 2020 at 05:14:36PM +0200, Thomas Zimmermann wrote:
> > At least sparc64 requires I/O-specific access to framebuffers. This
> > patch updates the fbdev console accordingly.
> >
> > For drivers with direct access to the framebuffer memory, the callback
> > functions in struct fb_ops test for the type of memory and call the rsp
> > fb_sys_ of fb_cfb_ functions.
> >
> > For drivers that employ a shadow buffer, fbdev's blit function retrieves
> > the framebuffer address as struct dma_buf_map, and uses dma_buf_map
> > interfaces to access the buffer.
> >
> > The bochs driver on sparc64 uses a workaround to flag the framebuffer as
> > I/O memory and avoid a HW exception. With the introduction of struct
> > dma_buf_map, this is not required any longer. The patch removes the rsp
> > code from both, bochs and fbdev.
> >
> > Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>

Argh, I accidentally hit send before finishing this ...

> > ---
> > drivers/gpu/drm/bochs/bochs_kms.c | 1 -
> > drivers/gpu/drm/drm_fb_helper.c | 217 ++++++++++++++++++++++++++++--
> > include/drm/drm_mode_config.h | 12 --
> > include/linux/dma-buf-map.h | 72 ++++++++--
> > 4 files changed, 265 insertions(+), 37 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/bochs/bochs_kms.c b/drivers/gpu/drm/bochs/bochs_kms.c
> > index 13d0d04c4457..853081d186d5 100644
> > --- a/drivers/gpu/drm/bochs/bochs_kms.c
> > +++ b/drivers/gpu/drm/bochs/bochs_kms.c
> > @@ -151,7 +151,6 @@ int bochs_kms_init(struct bochs_device *bochs)
> > bochs->dev->mode_config.preferred_depth = 24;
> > bochs->dev->mode_config.prefer_shadow = 0;
> > bochs->dev->mode_config.prefer_shadow_fbdev = 1;
> > - bochs->dev->mode_config.fbdev_use_iomem = true;
> > bochs->dev->mode_config.quirk_addfb_prefer_host_byte_order = true;
> >
> > bochs->dev->mode_config.funcs = &bochs_mode_funcs;
> > diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> > index 343a292f2c7c..f345a314a437 100644
> > --- a/drivers/gpu/drm/drm_fb_helper.c
> > +++ b/drivers/gpu/drm/drm_fb_helper.c
> > @@ -388,24 +388,22 @@ static void drm_fb_helper_resume_worker(struct work_struct *work)
> > }
> >
> > static void drm_fb_helper_dirty_blit_real(struct drm_fb_helper *fb_helper,
> > - struct drm_clip_rect *clip)
> > + struct drm_clip_rect *clip,
> > + struct dma_buf_map *dst)
> > {
> > struct drm_framebuffer *fb = fb_helper->fb;
> > unsigned int cpp = fb->format->cpp[0];
> > size_t offset = clip->y1 * fb->pitches[0] + clip->x1 * cpp;
> > void *src = fb_helper->fbdev->screen_buffer + offset;
> > - void *dst = fb_helper->buffer->map.vaddr + offset;
> > size_t len = (clip->x2 - clip->x1) * cpp;
> > unsigned int y;
> >
> > - for (y = clip->y1; y < clip->y2; y++) {
> > - if (!fb_helper->dev->mode_config.fbdev_use_iomem)
> > - memcpy(dst, src, len);
> > - else
> > - memcpy_toio((void __iomem *)dst, src, len);
> > + dma_buf_map_incr(dst, offset); /* go to first pixel within clip rect */
> >
> > + for (y = clip->y1; y < clip->y2; y++) {
> > + dma_buf_map_memcpy_to(dst, src, len);
> > + dma_buf_map_incr(dst, fb->pitches[0]);
> > src += fb->pitches[0];
> > - dst += fb->pitches[0];
> > }
> > }
> >
> > @@ -433,8 +431,9 @@ static void drm_fb_helper_dirty_work(struct work_struct *work)
> > ret = drm_client_buffer_vmap(helper->buffer, &map);
> > if (ret)
> > return;
> > - drm_fb_helper_dirty_blit_real(helper, &clip_copy);
> > + drm_fb_helper_dirty_blit_real(helper, &clip_copy, &map);
> > }
> > +
> > if (helper->fb->funcs->dirty)
> > helper->fb->funcs->dirty(helper->fb, NULL, 0, 0,
> > &clip_copy, 1);
> > @@ -771,6 +770,136 @@ void drm_fb_helper_sys_imageblit(struct fb_info *info,
> > }
> > EXPORT_SYMBOL(drm_fb_helper_sys_imageblit);
> >
> > +static ssize_t drm_fb_helper_cfb_read(struct fb_info *info, char __user *buf,
> > + size_t count, loff_t *ppos)
> > +{
> > + unsigned long p = *ppos;
> > + u8 *dst;
> > + u8 __iomem *src;
> > + int c, err = 0;
> > + unsigned long total_size;
> > + unsigned long alloc_size;
> > + ssize_t ret = 0;
> > +
> > + if (info->state != FBINFO_STATE_RUNNING)
> > + return -EPERM;
> > +
> > + total_size = info->screen_size;
> > +
> > + if (total_size == 0)
> > + total_size = info->fix.smem_len;
> > +
> > + if (p >= total_size)
> > + return 0;
> > +
> > + if (count >= total_size)
> > + count = total_size;
> > +
> > + if (count + p > total_size)
> > + count = total_size - p;
> > +
> > + src = (u8 __iomem *)(info->screen_base + p);
> > +
> > + alloc_size = min(count, PAGE_SIZE);
> > +
> > + dst = kmalloc(alloc_size, GFP_KERNEL);
> > + if (!dst)
> > + return -ENOMEM;
> > +
> > + while (count) {
> > + c = min(count, alloc_size);
> > +
> > + memcpy_fromio(dst, src, c);
> > + if (copy_to_user(buf, dst, c)) {
> > + err = -EFAULT;
> > + break;
> > + }
> > +
> > + src += c;
> > + *ppos += c;
> > + buf += c;
> > + ret += c;
> > + count -= c;
> > + }
> > +
> > + kfree(dst);
> > +
> > + if (err)
> > + return err;
> > +
> > + return ret;
> > +}
> > +
> > +static ssize_t drm_fb_helper_cfb_write(struct fb_info *info, const char __user *buf,
> > + size_t count, loff_t *ppos)
> > +{
> > + unsigned long p = *ppos;
> > + u8 *src;
> > + u8 __iomem *dst;
> > + int c, err = 0;
> > + unsigned long total_size;
> > + unsigned long alloc_size;
> > + ssize_t ret = 0;
> > +
> > + if (info->state != FBINFO_STATE_RUNNING)
> > + return -EPERM;
> > +
> > + total_size = info->screen_size;
> > +
> > + if (total_size == 0)
> > + total_size = info->fix.smem_len;
> > +
> > + if (p > total_size)
> > + return -EFBIG;
> > +
> > + if (count > total_size) {
> > + err = -EFBIG;
> > + count = total_size;
> > + }
> > +
> > + if (count + p > total_size) {
> > + /*
> > + * The framebuffer is too small. We do the
> > + * copy operation, but return an error code
> > + * afterwards. Taken from fbdev.
> > + */
> > + if (!err)
> > + err = -ENOSPC;
> > + count = total_size - p;
> > + }
> > +
> > + alloc_size = min(count, PAGE_SIZE);
> > +
> > + src = kmalloc(alloc_size, GFP_KERNEL);
> > + if (!src)
> > + return -ENOMEM;
> > +
> > + dst = (u8 __iomem *)(info->screen_base + p);
> > +
> > + while (count) {
> > + c = min(count, alloc_size);
> > +
> > + if (copy_from_user(src, buf, c)) {
> > + err = -EFAULT;
> > + break;
> > + }
> > + memcpy_toio(dst, src, c);
> > +
> > + dst += c;
> > + *ppos += c;
> > + buf += c;
> > + ret += c;
> > + count -= c;
> > + }
> > +
> > + kfree(src);
> > +
> > + if (err)
> > + return err;
> > +
> > + return ret;
> > +}

The duplication is a bit annoying here, but can't really be avoided. I
do think though we should maybe go a bit further, and have drm
implementations of this stuff instead of following fbdev concepts as
closely as possible. So here roughly:

- if we have a shadow fb, construct a dma_buf_map for that, otherwise
take the one from the driver
- have a full generic implementation using that one directly (and
checking size limits against the underlying gem buffer)
- ideally also with some testcases in the fbdev testcase we have (very
bare-bones right now) in igt

But I'm not really sure whether that's worth all the trouble. It's
just that the fbdev-ness here in this copied code sticks out a lot :-)

> > +
> > /**
> > * drm_fb_helper_cfb_fillrect - wrapper around cfb_fillrect
> > * @info: fbdev registered by the helper
> > @@ -2043,6 +2172,66 @@ static int drm_fbdev_fb_mmap(struct fb_info *info, struct vm_area_struct *vma)
> > return -ENODEV;
> > }
> >
> > +static ssize_t drm_fbdev_fb_read(struct fb_info *info, char __user *buf,
> > + size_t count, loff_t *ppos)
> > +{
> > + struct drm_fb_helper *fb_helper = info->par;
> > + struct drm_client_buffer *buffer = fb_helper->buffer;
> > +
> > + if (drm_fbdev_use_shadow_fb(fb_helper) || !buffer->map.is_iomem)
> > + return drm_fb_helper_sys_read(info, buf, count, ppos);
> > + else
> > + return drm_fb_helper_cfb_read(info, buf, count, ppos);
> > +}
> > +
> > +static ssize_t drm_fbdev_fb_write(struct fb_info *info, const char __user *buf,
> > + size_t count, loff_t *ppos)
> > +{
> > + struct drm_fb_helper *fb_helper = info->par;
> > + struct drm_client_buffer *buffer = fb_helper->buffer;
> > +
> > + if (drm_fbdev_use_shadow_fb(fb_helper) || !buffer->map.is_iomem)
> > + return drm_fb_helper_sys_write(info, buf, count, ppos);
> > + else
> > + return drm_fb_helper_cfb_write(info, buf, count, ppos);
> > +}
> > +
> > +static void drm_fbdev_fb_fillrect(struct fb_info *info,
> > + const struct fb_fillrect *rect)
> > +{
> > + struct drm_fb_helper *fb_helper = info->par;
> > + struct drm_client_buffer *buffer = fb_helper->buffer;
> > +
> > + if (drm_fbdev_use_shadow_fb(fb_helper) || !buffer->map.is_iomem)
> > + drm_fb_helper_sys_fillrect(info, rect);
> > + else
> > + drm_fb_helper_cfb_fillrect(info, rect);
> > +}
> > +
> > +static void drm_fbdev_fb_copyarea(struct fb_info *info,
> > + const struct fb_copyarea *area)
> > +{
> > + struct drm_fb_helper *fb_helper = info->par;
> > + struct drm_client_buffer *buffer = fb_helper->buffer;
> > +
> > + if (drm_fbdev_use_shadow_fb(fb_helper) || !buffer->map.is_iomem)
> > + drm_fb_helper_sys_copyarea(info, area);
> > + else
> > + drm_fb_helper_cfb_copyarea(info, area);
> > +}
> > +
> > +static void drm_fbdev_fb_imageblit(struct fb_info *info,
> > + const struct fb_image *image)
> > +{
> > + struct drm_fb_helper *fb_helper = info->par;
> > + struct drm_client_buffer *buffer = fb_helper->buffer;
> > +
> > + if (drm_fbdev_use_shadow_fb(fb_helper) || !buffer->map.is_iomem)
> > + drm_fb_helper_sys_imageblit(info, image);
> > + else
> > + drm_fb_helper_cfb_imageblit(info, image);
> > +}

I think a todo.rst entry to make the new generic functions the real ones, and
drivers not using the sys/cfb ones anymore would be a good addition.
It's kinda covered by the move to the generic helpers, but maybe we
can convert a few more drivers over to these here. Would also allow us
to maybe flatten the code a bit and use more of the dma_buf_map stuff
directly (instead of reusing crusty fbdev code written 20 years ago or
so).

> > +
> > static const struct fb_ops drm_fbdev_fb_ops = {
> > .owner = THIS_MODULE,
> > DRM_FB_HELPER_DEFAULT_OPS,
> > @@ -2050,11 +2239,11 @@ static const struct fb_ops drm_fbdev_fb_ops = {
> > .fb_release = drm_fbdev_fb_release,
> > .fb_destroy = drm_fbdev_fb_destroy,
> > .fb_mmap = drm_fbdev_fb_mmap,
> > - .fb_read = drm_fb_helper_sys_read,
> > - .fb_write = drm_fb_helper_sys_write,
> > - .fb_fillrect = drm_fb_helper_sys_fillrect,
> > - .fb_copyarea = drm_fb_helper_sys_copyarea,
> > - .fb_imageblit = drm_fb_helper_sys_imageblit,
> > + .fb_read = drm_fbdev_fb_read,
> > + .fb_write = drm_fbdev_fb_write,
> > + .fb_fillrect = drm_fbdev_fb_fillrect,
> > + .fb_copyarea = drm_fbdev_fb_copyarea,
> > + .fb_imageblit = drm_fbdev_fb_imageblit,
> > };
> >
> > static struct fb_deferred_io drm_fbdev_defio = {
> > diff --git a/include/drm/drm_mode_config.h b/include/drm/drm_mode_config.h
> > index 5ffbb4ed5b35..ab424ddd7665 100644
> > --- a/include/drm/drm_mode_config.h
> > +++ b/include/drm/drm_mode_config.h
> > @@ -877,18 +877,6 @@ struct drm_mode_config {
> > */
> > bool prefer_shadow_fbdev;
> >
> > - /**
> > - * @fbdev_use_iomem:
> > - *
> > - * Set to true if framebuffer reside in iomem.
> > - * When set to true memcpy_toio() is used when copying the framebuffer in
> > - * drm_fb_helper.drm_fb_helper_dirty_blit_real().
> > - *
> > - * FIXME: This should be replaced with a per-mapping is_iomem
> > - * flag (like ttm does), and then used everywhere in fbdev code.
> > - */
> > - bool fbdev_use_iomem;
> > -
> > /**
> > * @quirk_addfb_prefer_xbgr_30bpp:
> > *
> > diff --git a/include/linux/dma-buf-map.h b/include/linux/dma-buf-map.h

I think the below should be split out as a prep patch.

> > index 2e8bbecb5091..6ca0f304dda2 100644
> > --- a/include/linux/dma-buf-map.h
> > +++ b/include/linux/dma-buf-map.h
> > @@ -32,6 +32,14 @@
> > * accessing the buffer. Use the returned instance and the helper functions
> > * to access the buffer's memory in the correct way.
> > *
> > + * The type :c:type:`struct dma_buf_map <dma_buf_map>` and its helpers are
> > + * actually independent from the dma-buf infrastructure. When sharing buffers
> > + * among devices, drivers have to know the location of the memory to access
> > + * the buffers in a safe way. :c:type:`struct dma_buf_map <dma_buf_map>`
> > + * solves this problem for dma-buf and its users. If other drivers or
> > + * sub-systems require similar functionality, the type could be generalized
> > + * and moved to a more prominent header file.
> > + *
> > * Open-coding access to :c:type:`struct dma_buf_map <dma_buf_map>` is
> > * considered bad style. Rather then accessing its fields directly, use one
> > * of the provided helper functions, or implement your own. For example,
> > @@ -51,6 +59,14 @@
> > *
> > * dma_buf_map_set_vaddr_iomem(&map. 0xdeadbeaf);
> > *
> > + * Instances of struct dma_buf_map do not have to be cleaned up, but
> > + * can be cleared to NULL with dma_buf_map_clear(). Cleared mappings
> > + * always refer to system memory.
> > + *
> > + * .. code-block:: c
> > + *
> > + * dma_buf_map_clear(&map);
> > + *
> > * Test if a mapping is valid with either dma_buf_map_is_set() or
> > * dma_buf_map_is_null().
> > *
> > @@ -73,17 +89,19 @@
> > * if (dma_buf_map_is_equal(&sys_map, &io_map))
> > * // always false
> > *
> > - * Instances of struct dma_buf_map do not have to be cleaned up, but
> > - * can be cleared to NULL with dma_buf_map_clear(). Cleared mappings
> > - * always refer to system memory.
> > + * A set up instance of struct dma_buf_map can be used to access or manipulate
> > + * the buffer memory. Depending on the location of the memory, the provided
> > + * helpers will pick the correct operations. Data can be copied into the memory
> > + * with dma_buf_map_memcpy_to(). The address can be manipulated with
> > + * dma_buf_map_incr().
> > *
> > - * The type :c:type:`struct dma_buf_map <dma_buf_map>` and its helpers are
> > - * actually independent from the dma-buf infrastructure. When sharing buffers
> > - * among devices, drivers have to know the location of the memory to access
> > - * the buffers in a safe way. :c:type:`struct dma_buf_map <dma_buf_map>`
> > - * solves this problem for dma-buf and its users. If other drivers or
> > - * sub-systems require similar functionality, the type could be generalized
> > - * and moved to a more prominent header file.
> > + * .. code-block:: c
> > + *
> > + * const void *src = ...; // source buffer
> > + * size_t len = ...; // length of src
> > + *
> > + * dma_buf_map_memcpy_to(&map, src, len);
> > + * dma_buf_map_incr(&map, len); // go to first byte after the memcpy
> > */
> >
> > /**
> > @@ -210,4 +228,38 @@ static inline void dma_buf_map_clear(struct dma_buf_map *map)
> > }
> > }
> >
> > +/**
> > + * dma_buf_map_memcpy_to - Memcpy into dma-buf mapping
> > + * @dst: The dma-buf mapping structure
> > + * @src: The source buffer
> > + * @len: The number of byte in src
> > + *
> > + * Copies data into a dma-buf mapping. The source buffer is in system
> > + * memory. Depending on the buffer's location, the helper picks the correct
> > + * method of accessing the memory.
> > + */
> > +static inline void dma_buf_map_memcpy_to(struct dma_buf_map *dst, const void *src, size_t len)
> > +{
> > + if (dst->is_iomem)
> > + memcpy_toio(dst->vaddr_iomem, src, len);
> > + else
> > + memcpy(dst->vaddr, src, len);
> > +}
> > +
> > +/**
> > + * dma_buf_map_incr - Increments the address stored in a dma-buf mapping
> > + * @map: The dma-buf mapping structure
> > + * @incr: The number of bytes to increment
> > + *
> > + * Increments the address stored in a dma-buf mapping. Depending on the
> > + * buffer's location, the correct value will be updated.
> > + */
> > +static inline void dma_buf_map_incr(struct dma_buf_map *map, size_t incr)
> > +{
> > + if (map->is_iomem)
> > + map->vaddr_iomem += incr;
> > + else
> > + map->vaddr += incr;
> > +}
> > +
> > #endif /* __DMA_BUF_MAP_H__ */
> > --
> > 2.28.0

Aside from the details I think looks all reasonable.
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation