Patch "soc/fsl/qe: round brg_freq to 1kHz granularity" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

soc/fsl/qe: round brg_freq to 1kHz granularity

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
soc-fsl-qe-round-brg_freq-to-1khz-granularity.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Valentin Longchamp <[email protected]>
Date: Fri, 17 Feb 2017 11:29:45 +0100
Subject: soc/fsl/qe: round brg_freq to 1kHz granularity

From: Valentin Longchamp <[email protected]>

[ Upstream commit 2ccf80b7566cc035d903dd0ac5d7ebd25c2c1060 ]

Because of integer computation rounding in u-boot (that sets the QE brg-frequency DTS prop), the clk value is 99999999 Hz even though it is 100 MHz.

When setting brg clks that are exact divisors of 100 MHz, this small differnce plays a role and can result in lower clks to be output (for instance 20 MHz - divide by 5 - results in 16.666 MHz - divide by 6).

This patch fixes that by "forcing" the brg_clk to the nearest kHz when the difference is below 2 integer rounding errors (i.e. 4).

---
 drivers/soc/fsl/qe/qe.c |   13 +++++++++++++
 1 file changed, 13 insertions(+)

@@ -163,11 +163,15 @@ EXPORT_SYMBOL(qe_issue_cmd);
  */
 static unsigned int brg_clk = 0;
 
+#define CLK_GRAN	(1000)
+#define CLK_GRAN_LIMIT	(5)
+
 unsigned int qe_get_brg_clk(void)
 {
 	struct device_node *qe;
 	int size;
 	const u32 *prop;
+	unsigned int mod;
 
 	if (brg_clk)
 		return brg_clk;

@@ -185,6 +189,15 @@ unsigned int qe_get_brg_clk(void)
 
 	of_node_put(qe);
 
+	/* round this if near to a multiple of CLK_GRAN */
+	mod = brg_clk % CLK_GRAN;
+	if (mod) {
+		if (mod < CLK_GRAN_LIMIT)
+			brg_clk -= mod;
+		else if (mod > (CLK_GRAN - CLK_GRAN_LIMIT))
+			brg_clk += CLK_GRAN - mod;
+	}
+
 	return brg_clk;
 }
 EXPORT_SYMBOL(qe_get_brg_clk);

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/soc-fsl-qe-round-brg_freq-to-1khz-granularity.patch