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authorDoug Anderson <dianders@chromium.org>2014-04-30 19:44:07 +0200
committerLee Jones <lee.jones@linaro.org>2014-06-03 09:11:48 +0200
commit9c0b54a120348813de16be935d2e8a3e0e8e4a8b (patch)
tree1973af48d563e00de799a59f41ebe94a69b90979 /drivers/mfd/cros_ec_spi.c
parentmfd: cros_ec: spi: Make the cros_ec_spi timeout more reliable (diff)
downloadlinux-9c0b54a120348813de16be935d2e8a3e0e8e4a8b.tar.xz
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mfd: cros_ec: spi: Increase cros_ec_spi deadline from 5ms to 100ms
We're adding i2c tunneling to the list of things that goes over cros_ec. i2c tunneling can be slooooooow, so increase our deadline to 100ms to account for that. Signed-off-by: Doug Anderson <dianders@chromium.org> Reviewed-by: Simon Glass <sjg@chromium.org> Tested-by: Andrew Bresticker <abrestic@chromium.org> Tested-by: Stephen Warren <swarren@nvidia.com> Signed-off-by: Lee Jones <lee.jones@linaro.org>
Diffstat (limited to 'drivers/mfd/cros_ec_spi.c')
-rw-r--r--drivers/mfd/cros_ec_spi.c24
1 files changed, 16 insertions, 8 deletions
diff --git a/drivers/mfd/cros_ec_spi.c b/drivers/mfd/cros_ec_spi.c
index 4f863c346547..0b8d32829166 100644
--- a/drivers/mfd/cros_ec_spi.c
+++ b/drivers/mfd/cros_ec_spi.c
@@ -39,14 +39,22 @@
#define EC_MSG_PREAMBLE_COUNT 32
/*
- * We must get a response from the EC in 5ms. This is a very long
- * time, but the flash write command can take 2-3ms. The EC command
- * processing is currently not very fast (about 500us). We could
- * look at speeding this up and making the flash write command a
- * 'slow' command, requiring a GET_STATUS wait loop, like flash
- * erase.
- */
-#define EC_MSG_DEADLINE_MS 5
+ * Allow for a long time for the EC to respond. We support i2c
+ * tunneling and support fairly long messages for the tunnel (249
+ * bytes long at the moment). If we're talking to a 100 kHz device
+ * on the other end and need to transfer ~256 bytes, then we need:
+ * 10 us/bit * ~10 bits/byte * ~256 bytes = ~25ms
+ *
+ * We'll wait 4 times that to handle clock stretching and other
+ * paranoia.
+ *
+ * It's pretty unlikely that we'll really see a 249 byte tunnel in
+ * anything other than testing. If this was more common we might
+ * consider having slow commands like this require a GET_STATUS
+ * wait loop. The 'flash write' command would be another candidate
+ * for this, clocking in at 2-3ms.
+ */
+#define EC_MSG_DEADLINE_MS 100
/*
* Time between raising the SPI chip select (for the end of a