[PATCH 5/9] drm: bridge/dw_hdmi: avoid being recursive in N calculation

[Doug Anderson]

Russell,

On Sat, Aug 8, 2015 at 9:10 AM, Russell King
 wrote:
> There's no need to be recursive when computing the N value for the ACR
> packet - we can instead calculate the multiplier prior to our switch()
> based lookup, and multiply the N value appropriately afterwards.
>
> Signed-off-by: Russell King 
> ---
>  drivers/gpu/drm/bridge/dw_hdmi.c | 25 +
>  1 file changed, 9 insertions(+), 16 deletions(-)

For what it's worth, I backported this change into my local 3.14-based
tree and it worked for me.  It also looks good to me.

Reviewed-by: Douglas Anderson 
Tested-by: Douglas Anderson 

[PATCH 5/9] drm: bridge/dw_hdmi: avoid being recursive in N calculation

[Russell King]

There's no need to be recursive when computing the N value for the ACR
packet - we can instead calculate the multiplier prior to our switch()
based lookup, and multiply the N value appropriately afterwards.

Signed-off-by: Russell King 
---
 drivers/gpu/drm/bridge/dw_hdmi.c | 25 +
 1 file changed, 9 insertions(+), 16 deletions(-)

diff --git a/drivers/gpu/drm/bridge/dw_hdmi.c b/drivers/gpu/drm/bridge/dw_hdmi.c
index a8b243278774..f0e6059f818a 100644
--- a/drivers/gpu/drm/bridge/dw_hdmi.c
+++ b/drivers/gpu/drm/bridge/dw_hdmi.c
@@ -221,6 +221,12 @@ static unsigned int hdmi_compute_n(unsigned int freq, 
unsigned long pixel_clk,
   unsigned int ratio)
 {
unsigned int n = (128 * freq) / 1000;
+   unsigned int mult = 1;
+
+   while (freq > 48000) {
+   mult *= 2;
+   freq /= 2;
+   }

switch (freq) {
case 32000:
@@ -232,6 +238,7 @@ static unsigned int hdmi_compute_n(unsigned int freq, 
unsigned long pixel_clk,
n = 11648;
else
n = 4096;
+   n *= mult;
break;

case 44100:
@@ -243,6 +250,7 @@ static unsigned int hdmi_compute_n(unsigned int freq, 
unsigned long pixel_clk,
n = (ratio == 150) ? 17836 : 8918;
else
n = 6272;
+   n *= mult;
break;

case 48000:
@@ -256,22 +264,7 @@ static unsigned int hdmi_compute_n(unsigned int freq, 
unsigned long pixel_clk,
n = (ratio == 150) ? 11648 : 5824;
else
n = 6144;
-   break;
-
-   case 88200:
-   n = hdmi_compute_n(44100, pixel_clk, ratio) * 2;
-   break;
-
-   case 96000:
-   n = hdmi_compute_n(48000, pixel_clk, ratio) * 2;
-   break;
-
-   case 176400:
-   n = hdmi_compute_n(44100, pixel_clk, ratio) * 4;
-   break;
-
-   case 192000:
-   n = hdmi_compute_n(48000, pixel_clk, ratio) * 4;
+   n *= mult;
break;

default:
-- 
2.1.0