linux-kernel - [v0.1 PATCH 7/7] mmc: tmio: refactor CLK

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Date:   Tue,  7 Aug 2018 15:17:22 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Wolfram Sang <wsa+renesas@...g-engineering.com>,
        linux-mmc@...r.kernel.org
Cc:     Ulf Hansson <ulf.hansson@...aro.org>,
        linux-renesas-soc@...r.kernel.org,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Jassi Brar <jaswinder.singh@...aro.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        linux-kernel@...r.kernel.org
Subject: [v0.1 PATCH 7/7] mmc: tmio: refactor CLK_CTL bit calculation

  for (clk = 0x80000080; new_clock >= (clock << 1); clk >>= 1)
          clock <<= 1;

... is too tricky, hence I replaced with

  roundup_pow_of_two(divisor) >> 2

'(clk >> 22) & 0x1' is the bit test for the 1/1 divisor, but
it is not clear.  'divisor <= 1' is easier to understand.

Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
---

 drivers/mmc/host/tmio_mmc.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/drivers/mmc/host/tmio_mmc.c b/drivers/mmc/host/tmio_mmc.c
index b031a77..e04c322 100644
--- a/drivers/mmc/host/tmio_mmc.c
+++ b/drivers/mmc/host/tmio_mmc.c
@@ -48,19 +48,27 @@ static void tmio_mmc_clk_stop(struct tmio_mmc_host *host)
 static void tmio_mmc_set_clock(struct tmio_mmc_host *host,
 			       unsigned int new_clock)
 {
-	u32 clk = 0, clock;
+	unsigned int clock, divisor;
+	u32 clk = 0;
+	int clk_sel;
 
 	if (new_clock == 0) {
 		tmio_mmc_clk_stop(host);
 		return;
 	}
 
-	clock = host->mmc->f_min;
+	divisor = host->pdata->hclk / new_clock;
 
-	for (clk = 0x80000080; new_clock >= (clock << 1); clk >>= 1)
-		clock <<= 1;
+	if (divisor <= 1) {
+		clk_sel = 1;
+		clk = 0;
+	} else {
+		clk_sel = 0;
+		/* bit7 set: 1/512, ... bit0 set:1/4, all bits clear: 1/2 */
+		clk = roundup_pow_of_two(divisor) >> 2;
+	}
 
-	host->pdata->set_clk_div(host->pdev, (clk >> 22) & 1);
+	host->pdata->set_clk_div(host->pdev, clk_sel);
 
 	sd_ctrl_write16(host, CTL_SD_CARD_CLK_CTL, ~CLK_CTL_SCLKEN &
 			sd_ctrl_read16(host, CTL_SD_CARD_CLK_CTL));
-- 
2.7.4