Re: [PATCH v4 2/7] media: s5p-mfc: use generic reserved memory bindings

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Hello,


On 2016-05-25 19:36, Rob Herring wrote:
On Wed, May 25, 2016 at 11:18:59AM -0400, Javier Martinez Canillas wrote:
Hello Marek,

On 05/24/2016 09:31 AM, Marek Szyprowski wrote:
Use generic reserved memory bindings and mark old, custom properties
as obsoleted.

Signed-off-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
---
  .../devicetree/bindings/media/s5p-mfc.txt          | 39 +++++++++++++++++-----
  1 file changed, 31 insertions(+), 8 deletions(-)

diff --git a/Documentation/devicetree/bindings/media/s5p-mfc.txt b/Documentation/devicetree/bindings/media/s5p-mfc.txt
index 2d5787e..92c94f5 100644
--- a/Documentation/devicetree/bindings/media/s5p-mfc.txt
+++ b/Documentation/devicetree/bindings/media/s5p-mfc.txt
@@ -21,15 +21,18 @@ Required properties:
    - clock-names : from common clock binding: must contain "mfc",
  		  corresponding to entry in the clocks property.
- - samsung,mfc-r : Base address of the first memory bank used by MFC
-		    for DMA contiguous memory allocation and its size.
-
-  - samsung,mfc-l : Base address of the second memory bank used by MFC
-		    for DMA contiguous memory allocation and its size.
-
  Optional properties:
    - power-domains : power-domain property defined with a phandle
  			   to respective power domain.
+  - memory-region : from reserved memory binding: phandles to two reserved
+	memory regions, first is for "left" mfc memory bus interfaces,
+	second if for the "right" mfc memory bus, used when no SYSMMU
+	support is available
+
+Obsolete properties:
+  - samsung,mfc-r, samsung,mfc-l : support removed, please use memory-region
+	property instead
+

I wonder if we should maintain backward compatibility for this driver
since s5p-mfc memory allocation won't work with an old FDT if support
for the old properties are removed.
Well, minimally the commit log should indicate that compatibility is
being broken.

Compatibility is only partially broken. I add this to the commit message. Old bindings will still work with the new driver when IOMMU is enabled - in such case reserved memory regions are ignored so this should not be a big issue. Using IOMMU also increases total memory space for the video buffers without wasting it as 'reserved'. Hope that once those patches are merged, the IOMMU can be finally enabled in the exynos_defconfig.

Best regards
--
Marek Szyprowski, PhD
Samsung R&D Institute Poland

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