From: Doug Anderson <dianders@chromium.org>
To: lee.jones@linaro.org, swarren@nvidia.com, wsa@the-dreams.de
Cc: abrestic@chromium.org, dgreid@chromium.org, olof@lixom.net,
sjg@chromium.org, linux-samsung-soc@vger.kernel.org,
linux-tegra@vger.kernel.org,
Doug Anderson <dianders@chromium.org>,
sameo@linux.intel.com, linux-kernel@vger.kernel.org
Subject: [PATCH v2 4/7] mfd: cros_ec: spi: Increase cros_ec_spi deadline from 5ms to 100ms
Date: Tue, 22 Apr 2014 09:45:51 -0700 [thread overview]
Message-ID: <1398185154-19404-5-git-send-email-dianders@chromium.org> (raw)
In-Reply-To: <1398185154-19404-1-git-send-email-dianders@chromium.org>
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>
---
Changes in v2: None
drivers/mfd/cros_ec_spi.c | 24 ++++++++++++++++--------
1 file changed, 16 insertions(+), 8 deletions(-)
diff --git a/drivers/mfd/cros_ec_spi.c b/drivers/mfd/cros_ec_spi.c
index 4f863c3..0b8d328 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
--
1.9.1.423.g4596e3a
next prev parent reply other threads:[~2014-04-22 16:48 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-04-22 16:45 [PATCH v2 0/7] Add cros_ec changes for newer boards Doug Anderson
2014-04-22 16:45 ` [PATCH v2 1/7] mfd: cros_ec: spi: calculate delay between transfers correctly Doug Anderson
2014-04-23 12:33 ` Lee Jones
2014-04-22 16:45 ` [PATCH v2 2/7] mfd: cros_ec: spi: Add mutex to cros_ec_spi Doug Anderson
2014-04-23 12:34 ` Lee Jones
2014-04-22 16:45 ` [PATCH v2 3/7] mfd: cros_ec: spi: Make the cros_ec_spi timeout more reliable Doug Anderson
2014-04-23 12:35 ` Lee Jones
2014-04-22 16:45 ` Doug Anderson [this message]
2014-04-23 12:36 ` [PATCH v2 4/7] mfd: cros_ec: spi: Increase cros_ec_spi deadline from 5ms to 100ms Lee Jones
2014-04-22 16:45 ` [PATCH v2 5/7] mfd: cros_ec: Sync to the latest cros_ec_commands.h from EC sources Doug Anderson
2014-04-23 12:36 ` Lee Jones
2014-04-22 16:45 ` [PATCH v2 6/7] i2c: ChromeOS EC tunnel driver Doug Anderson
2014-04-23 12:37 ` Lee Jones
2014-04-29 12:33 ` Wolfram Sang
2014-04-22 16:45 ` [PATCH v2 7/7] ARM: tegra: Add the EC i2c tunnel to tegra124-venice2 Doug Anderson
2014-04-23 12:32 ` [PATCH v2 0/7] Add cros_ec changes for newer boards Lee Jones
2014-04-23 16:20 ` Stephen Warren
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