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

Daniel Vetter
2020-10-02T18:05:13Z

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>
> ---
> 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;
> +}
> +
> /**
> * 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 to make the new generic functions the real ones, and
drivers not using the sys/cfb ones anymore would be a good addition.

> +
> 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
>

--
Daniel Vetter
Software Engineer, Intel Corporation