This is a note to let you know that I've just added the patch titled
spi: mvebu: fix baudrate calculation for armada variant
to the 4.4-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:
spi-mvebu-fix-baudrate-calculation-for-armada-variant.patch
and it can be found in the queue-4.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 7243e0b20729d372e97763617a7a9c89f29b33e1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Uwe=20Kleine-K=C3=B6nig?= <uwe@xxxxxxxxxxxxxxxxx>
Date: Thu, 8 Dec 2016 17:37:08 +0100
Subject: spi: mvebu: fix baudrate calculation for armada variant
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
From: Uwe Kleine-König <uwe@xxxxxxxxxxxxxxxxx>
commit 7243e0b20729d372e97763617a7a9c89f29b33e1 upstream.
The calculation of SPR and SPPR doesn't round correctly at several
places which might result in baud rates that are too big. For example
with tclk_hz = 250000001 and target rate 25000000 it determined a
divider of 10 which is wrong.
Instead of fixing all the corner cases replace the calculation by an
algorithm without a loop which should even be quicker to execute apart
from being correct.
Fixes: df59fa7f4bca ("spi: orion: support armada extended baud rates")
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/spi/spi-orion.c | 83 +++++++++++++++++++++++++++++++-----------------
1 file changed, 54 insertions(+), 29 deletions(-)
--- a/drivers/spi/spi-orion.c
+++ b/drivers/spi/spi-orion.c
@@ -127,37 +127,62 @@ static int orion_spi_baudrate_set(struct
tclk_hz = clk_get_rate(orion_spi->clk);
if (devdata->typ == ARMADA_SPI) {
- unsigned int clk, spr, sppr, sppr2, err;
- unsigned int best_spr, best_sppr, best_err;
-
- best_err = speed;
- best_spr = 0;
- best_sppr = 0;
-
- /* Iterate over the valid range looking for best fit */
- for (sppr = 0; sppr < 8; sppr++) {
- sppr2 = 0x1 << sppr;
-
- spr = tclk_hz / sppr2;
- spr = DIV_ROUND_UP(spr, speed);
- if ((spr == 0) || (spr > 15))
- continue;
-
- clk = tclk_hz / (spr * sppr2);
- err = speed - clk;
-
- if (err < best_err) {
- best_spr = spr;
- best_sppr = sppr;
- best_err = err;
- }
+ /*
+ * Given the core_clk (tclk_hz) and the target rate (speed) we
+ * determine the best values for SPR (in [0 .. 15]) and SPPR (in
+ * [0..7]) such that
+ *
+ * core_clk / (SPR * 2 ** SPPR)
+ *
+ * is as big as possible but not bigger than speed.
+ */
+
+ /* best integer divider: */
+ unsigned divider = DIV_ROUND_UP(tclk_hz, speed);
+ unsigned spr, sppr;
+
+ if (divider < 16) {
+ /* This is the easy case, divider is less than 16 */
+ spr = divider;
+ sppr = 0;
+
+ } else {
+ unsigned two_pow_sppr;
+ /*
+ * Find the highest bit set in divider. This and the
+ * three next bits define SPR (apart from rounding).
+ * SPPR is then the number of zero bits that must be
+ * appended:
+ */
+ sppr = fls(divider) - 4;
+
+ /*
+ * As SPR only has 4 bits, we have to round divider up
+ * to the next multiple of 2 ** sppr.
+ */
+ two_pow_sppr = 1 << sppr;
+ divider = (divider + two_pow_sppr - 1) & -two_pow_sppr;
+
+ /*
+ * recalculate sppr as rounding up divider might have
+ * increased it enough to change the position of the
+ * highest set bit. In this case the bit that now
+ * doesn't make it into SPR is 0, so there is no need to
+ * round again.
+ */
+ sppr = fls(divider) - 4;
+ spr = divider >> sppr;
+
+ /*
+ * Now do range checking. SPR is constructed to have a
+ * width of 4 bits, so this is fine for sure. So we
+ * still need to check for sppr to fit into 3 bits:
+ */
+ if (sppr > 7)
+ return -EINVAL;
}
- if ((best_sppr == 0) && (best_spr == 0))
- return -EINVAL;
-
- prescale = ((best_sppr & 0x6) << 5) |
- ((best_sppr & 0x1) << 4) | best_spr;
+ prescale = ((sppr & 0x6) << 5) | ((sppr & 0x1) << 4) | spr;
} else {
/*
* the supported rates are: 4,6,8...30
Patches currently in stable-queue which might be from uwe@xxxxxxxxxxxxxxxxx are
queue-4.4/spi-mvebu-fix-baudrate-calculation-for-armada-variant.patch
--
To unsubscribe from this list: send the line "unsubscribe stable" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html