drm/tinydrm: mipi-dbi: Fix unbalanced DMA access

If we return here and import_attach is true, then dma_buf_end_cpu_access() will not be called balance dma_buf_begin_cpu_access().

Fix by setting ret instead of returning.

Signed-off-by David Lechner <[email protected]>

---

  drivers/gpu/drm/tinydrm/mipi-dbi.c | 3 ++-
  1 file changed, 2 insertions(+), 1 deletion(-)

drivers/gpu/drm/tinydrm/mipi-dbi.c +0 -0

index c83eeb7..e10fa4b 100644

If we return here and import_attach is true, then dma_buf_end_cpu_access() will not be called balance dma_buf_begin_cpu_access().

Fix by setting ret instead of returning.

Signed-off-by David Lechner <[email protected]>

---
  drivers/gpu/drm/tinydrm/mipi-dbi.c | 3 ++-
  1 file changed, 2 insertions(+), 1 deletion(-)

drivers/gpu/drm/tinydrm/mipi-dbi.c +0 -0

index c83eeb7..e10fa4b 100644

Quoted 16 lines

If we return here and import_attach is true, then dma_buf_end_cpu_access() will not be called balance dma_buf_begin_cpu_access().

Fix by setting ret instead of returning.

Signed-off-by David Lechner <[email protected]>

---
  drivers/gpu/drm/tinydrm/mipi-dbi.c | 3 ++-
  1 file changed, 2 insertions(+), 1 deletion(-)

drivers/gpu/drm/tinydrm/mipi-dbi.c +0 -0

index c83eeb7..e10fa4b 100644

drivers/gpu/drm/tinydrm/mipi-dbi.c static int mipi_dbi_buf_copy(void *dst, struct · line 190

Quoted 9 lines

drivers/gpu/drm/tinydrm/mipi-dbi.c +2 -1

@@ -183,7 +183,8 @@ static int mipi_dbi_buf_copy(void *dst, struct 
 drm_framebuffer *fb,
          dev_err_once(fb->dev->dev, "Format is not supported: %s\n",
                   drm_get_format_name(fb->format->format,
                           &format_name));
-        return -EINVAL;
+        ret = -EINVAL;
+        break;
      }
        if (import_attach)

I just realized that the next line here can mask ret.

    if (import_attach)
        ret = dma_buf_end_cpu_access(import_attach->dmabuf,
                         DMA_FROM_DEVICE);

So, we should either ignore the return value from dma_buf_end_cpu_access() always or add some logic to ignore it if ret is already an error.

In some of the other patches I have been sending, we have the same situation. I those, I have opted to just ignore the return value from dma_buf_end_cpu_access(). e.g...

    if (import_attach)
        dma_buf_end_cpu_access(import_attach->dmabuf, DMA_FROM_DEVICE);

Is this a reasonable thing to do?

Den 04.08.2017 00.41, skrev David Lechner:

Quoted 37 lines · David Lechner

Quoted 16 lines

If we return here and import_attach is true, then dma_buf_end_cpu_access() will not be called balance dma_buf_begin_cpu_access().

Fix by setting ret instead of returning.

Signed-off-by David Lechner <[email protected]>

---
  drivers/gpu/drm/tinydrm/mipi-dbi.c | 3 ++-
  1 file changed, 2 insertions(+), 1 deletion(-)

drivers/gpu/drm/tinydrm/mipi-dbi.c +0 -0

index c83eeb7..e10fa4b 100644

drivers/gpu/drm/tinydrm/mipi-dbi.c static int mipi_dbi_buf_copy(void *dst, struct · line 190

Quoted 9 lines

drivers/gpu/drm/tinydrm/mipi-dbi.c +2 -1

@@ -183,7 +183,8 @@ static int mipi_dbi_buf_copy(void *dst, struct 
 drm_framebuffer *fb,
          dev_err_once(fb->dev->dev, "Format is not supported: %s\n",
                   drm_get_format_name(fb->format->format,
                           &format_name));
-        return -EINVAL;
+        ret = -EINVAL;
+        break;
      }
        if (import_attach)

I just realized that the next line here can mask ret.

    if (import_attach)
        ret = dma_buf_end_cpu_access(import_attach->dmabuf,
                         DMA_FROM_DEVICE);

So, we should either ignore the return value from dma_buf_end_cpu_access() always or add some logic to ignore it if ret is already an error.

Quoted 7 lines

In some of the other patches I have been sending, we have the same situation. I those, I have opted to just ignore the return value from dma_buf_end_cpu_access(). e.g...

    if (import_attach)
        dma_buf_end_cpu_access(import_attach->dmabuf, DMA_FROM_DEVICE);

Is this a reasonable thing to do?

mipi_dbi_buf_copy() can be used by other rgb565 controllers, hence the format check I think. So when that happens, it can be moved to tinydrm-helpers.

Currently it's not possible to get an illegal format, since mipi-dbi only supports those two formats.
Userspace can't set an illegal format, beacuse it's checked:
drm_atomic_commit -> drm_atomic_check_only -> drm_atomic_plane_check -> drm_plane_check_pixel_format

So I think we can just leave this alone, or put the check before import_attach if you really want to put this straight.