[PATCH] OMAP: McBSP: Do not enable SRG in slave mode

[PATCH] OMAP: McBSP: Do not enable SRG in slave mode

[Peter Ujfalusi]

McBSP SRG (Sample Rate Generator) and FSG (Frame Sync
Generator) is only needed to be enabled, when McBSP
is master.
In McBSP slave mode, the SRG, and FSG can be kept disabled,
which might save some power at the end in this configuration.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@nokia.com>
---

Hello Jarkko,

I have tested this on OMAP3, but I think this should be
applicable for other OMAP versions as well.
When McBSP was slave the audio worked fine, when I left
the SRG, and FSG disabled.

 arch/arm/plat-omap/mcbsp.c |   13 ++++++++-----
 1 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/arch/arm/plat-omap/mcbsp.c b/arch/arm/plat-omap/mcbsp.c
index e31496e..ecbfe39 100644
--- a/arch/arm/plat-omap/mcbsp.c
+++ b/arch/arm/plat-omap/mcbsp.c
@@ -878,7 +878,7 @@ EXPORT_SYMBOL(omap_mcbsp_free);
 void omap_mcbsp_start(unsigned int id, int tx, int rx)
 {
 	struct omap_mcbsp *mcbsp;
-	int idle;
+	int enable_srg = 0;
 	u16 w;
 
 	if (!omap_mcbsp_check_valid_id(id)) {
@@ -893,10 +893,13 @@ void omap_mcbsp_start(unsigned int id, int tx, int rx)
 	mcbsp->rx_word_length = (MCBSP_READ_CACHE(mcbsp, RCR1) >> 5) & 0x7;
 	mcbsp->tx_word_length = (MCBSP_READ_CACHE(mcbsp, XCR1) >> 5) & 0x7;
 
-	idle = !((MCBSP_READ_CACHE(mcbsp, SPCR2) |
-			MCBSP_READ_CACHE(mcbsp, SPCR1)) & 1);
+	/* Only enable SRG, if McBSP is master */
+	w = MCBSP_READ_CACHE(mcbsp, PCR0);
+	if (w & (FSXM | FSRM | CLKXM | CLKRM))
+		enable_srg = !((MCBSP_READ_CACHE(mcbsp, SPCR2) |
+				MCBSP_READ_CACHE(mcbsp, SPCR1)) & 1);
 
-	if (idle) {
+	if (enable_srg) {
 		/* Start the sample generator */
 		w = MCBSP_READ_CACHE(mcbsp, SPCR2);
 		MCBSP_WRITE(mcbsp, SPCR2, w | (1 << 6));
@@ -919,7 +922,7 @@ void omap_mcbsp_start(unsigned int id, int tx, int rx)
 	 */
 	udelay(500);
 
-	if (idle) {
+	if (enable_srg) {
 		/* Start frame sync */
 		w = MCBSP_READ_CACHE(mcbsp, SPCR2);
 		MCBSP_WRITE(mcbsp, SPCR2, w | (1 << 7));
-- 
1.7.2.2

Re: [PATCH] OMAP: McBSP: Do not enable SRG in slave mode

[Jarkko Nikula]

On Tue, 31 Aug 2010 11:11:44 +0300
Peter Ujfalusi <peter.ujfalusi@nokia.com> wrote:

> McBSP SRG (Sample Rate Generator) and FSG (Frame Sync
> Generator) is only needed to be enabled, when McBSP
> is master.
> In McBSP slave mode, the SRG, and FSG can be kept disabled,
> which might save some power at the end in this configuration.
> 
> Signed-off-by: Peter Ujfalusi <peter.ujfalusi@nokia.com>
> ---
> 
> Hello Jarkko,
> 
> I have tested this on OMAP3, but I think this should be
> applicable for other OMAP versions as well.
> When McBSP was slave the audio worked fine, when I left
> the SRG, and FSG disabled.
> 
Sounds logical if there is no need to keep SRG and FSG active when
McBSP is slave. I tested this on N810.

Acked-by: Jarkko Nikula <jhnikula@gmail.com>

[APPLIED] [PATCH] OMAP: McBSP: Do not enable SRG in slave mode

[Tony Lindgren]

This patch has been applied to the linux-omap
by youw fwiendly patch wobot.

Branch in linux-omap: devel-omap-misc

Initial commit ID (Likely to change): d0db27786b9fabeac6cb330ccf127451c249af73

PatchWorks
http://patchwork.kernel.org/patch/144621/

Git (Likely to change, and takes a while to get mirrored)
http://git.kernel.org/?p=linux/kernel/git/tmlind/linux-omap-2.6.git;a=commit;h=d0db27786b9fabeac6cb330ccf127451c249af73