Hi, Guenter,

Thanks for your test and comment.


On Wed, 2017-06-21 at 14:14 -0700, Guenter Roeck wrote:

On Fri, May 19, 2017 at 05:57:23PM +0800, Bibby Hsieh wrote:

quoted

For some greater resolution, the rdma threshold
variable will overflow.

Signed-off-by: Bibby Hsieh <redacted>
---
 drivers/gpu/drm/mediatek/mtk_disp_rdma.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/mediatek/mtk_disp_rdma.c b/drivers/gpu/drm/mediatek/mtk_disp_rdma.c
index 0df05f9..9afdcd7 100644
--- a/drivers/gpu/drm/mediatek/mtk_disp_rdma.c
+++ b/drivers/gpu/drm/mediatek/mtk_disp_rdma.c

@@ -37,7 +37,7 @@
 #define DISP_REG_RDMA_FIFO_CON			0x0040
 #define RDMA_FIFO_UNDERFLOW_EN				BIT(31)
 #define RDMA_FIFO_PSEUDO_SIZE(bytes)			(((bytes) / 16) << 16)
-#define RDMA_OUTPUT_VALID_FIFO_THRESHOLD(bytes)		((bytes) / 16)
+#define RDMA_OUTPUT_VALID_FIFO_THRESHOLD(bytes) (((bytes) / 16) & 0x3ff)

I agree with the earlier comment; clamp_val() might be more appropriate here
and would avoid unexpected results.

Yep, It's a good suggestion to me, I will add clamp_val() to avoid
unexpected value, thanks.

quoted

 
 /**
  * struct mtk_disp_rdma - DISP_RDMA driver structure

@@ -109,7 +109,7 @@ static void mtk_rdma_config(struct mtk_ddp_comp *comp, unsigned int width,
 			    unsigned int height, unsigned int vrefresh,
 			    unsigned int bpc)
 {
-	unsigned int threshold;
+	unsigned long long threshold;
 	unsigned int reg;
 
 	rdma_update_bits(comp, DISP_REG_RDMA_SIZE_CON_0, 0xfff, width);

@@ -121,7 +121,8 @@ static void mtk_rdma_config(struct mtk_ddp_comp *comp, unsigned int width,
 	 * output threshold to 6 microseconds with 7/6 overhead to
 	 * account for blanking, and with a pixel depth of 4 bytes:
 	 */
-	threshold = width * height * vrefresh * 4 * 7 / 1000000;
+	threshold = (unsigned long long)width * height * vrefresh *
+		    4 * 7 / 1000000;

This is a 64 bit divide operation. It will result in a build failure
if compiled for a 32 bit kernel (eg arm:allmodconfig).

ERROR: "__aeabi_uldivmod" [drivers/gpu/drm/mediatek/mediatek-drm.ko] undefined!

Sorry about the lack of tests, I will change the divide operation to
div_u64 function, thanks for your suggestions.

Guenter

-- 
Bibby