linux-kernel - [PATCH] ASoC: fsl_ssi: Don't try to round-up for PM divisor calculation

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Date:	Sun, 15 Feb 2015 01:37:11 -0800
From:	Nicolin Chen <nicoleotsuka@...il.com>
To:	broonie@...nel.org
Cc:	alsa-devel@...a-project.org, lgirdwood@...il.com, tiwai@...e.de,
	perex@...ex.cz, linux-kernel@...r.kernel.org, timur@...i.org,
	mpa@...gutronix.de, shengjiu.wang@...escale.com,
	zidan.wang@...escale.com, scerveau@...tok.com
Subject: [PATCH] ASoC: fsl_ssi: Don't try to round-up for PM divisor calculation

According to i.MX6 Series Reference Manual, the formula to calculate
the sys clock is

sysclk rate = bclk rate * (div2 + 1) * (7 * psr + 1) * (pm + 1) * 2

Commit aafa85e71a75 ("ASoC: fsl_ssi: Add DAI master mode support for
SSI on i.MX series") added the divisor calculation which relies on
the clk_round_rate(). However, at that time, clk_round_rate() didn't
provide closest clock rates for some cases because it might not use
a correct rounding policy. So using the original formula (pm + 1) for
PM divisor was not able to give us a desired clock rate. And then we
used (pm + 2) to do the trick.

However, the clk-divider driver has been refined a lot since commit
b11d282dbea2 ("clk: divider: fix rate calculation for fractional rates")
Now using (pm + 2) trick would result an incorrect clock rate.

So this patch fixes the problem by removing the useless trick.

Reported-by: Stephane Cerveau <scerveau@...tok.com>
Signed-off-by: Nicolin Chen <nicoleotsuka@...il.com>
---

[ I also checked that only 3.18 stable tree has the refinements for
 clk-divider driver, so I guess it might not be able to apply to
 previous long-term trees if being treated as bug fix. -- Nicolin ]

 sound/soc/fsl/fsl_ssi.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sound/soc/fsl/fsl_ssi.c b/sound/soc/fsl/fsl_ssi.c
index d7365c5..3e7c644 100644
--- a/sound/soc/fsl/fsl_ssi.c
+++ b/sound/soc/fsl/fsl_ssi.c
@@ -603,7 +603,7 @@ static int fsl_ssi_set_bclk(struct snd_pcm_substream *substream,
 	factor = (div2 + 1) * (7 * psr + 1) * 2;

 	for (i = 0; i < 255; i++) {
-		tmprate = freq * factor * (i + 2);
+		tmprate = freq * factor * (i + 1);

 		if (baudclk_is_used)
 			clkrate = clk_get_rate(ssi_private->baudclk);
-- 
1.9.1

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