Sometimes kernel is trying to probe Fingerprint MCU (FPMCU) when it hasn't initialized SPI yet. This can happen because FPMCU is restarted during system boot and kernel can send message in short window eg. between sysjump to RW and SPI initialization.

Cc: stable@vger.kernel.org # 4.4+ Signed-off-by: Patryk Duda pdk@semihalf.com --- Fingerprint MCU is rebooted during system startup by AP firmware (coreboot). During cold boot kernel can query FPMCU in a window just after jump to RW section of firmware but before SPI is initialized. The window was shortened to <1ms, but it can't be eliminated completly.

Communication with FPMCU (and all devices based on EC) is bi-directional. When kernel sends message, EC will send EC_SPI* status codes. When EC is not able to process command one of bytes will be eg. EC_SPI_NOT_READY. This mechanism won't work when SPI is not initailized on EC side. In fact, buffer is filled with 0xFF bytes, so from kernel perspective device is not responding. To avoid this problem, we can query device once again. We are already waiting EC_MSG_DEADLINE_MS for response, so we can send command immediately.

Best regards, Patryk drivers/platform/chrome/cros_ec_proto.c | 12 ++++++++++++ 1 file changed, 12 insertions(+)

diff --git a/drivers/platform/chrome/cros_ec_proto.c b/drivers/platform/chrome/cros_ec_proto.c index aa7f7aa77297..3384631d21e2 100644 --- a/drivers/platform/chrome/cros_ec_proto.c +++ b/drivers/platform/chrome/cros_ec_proto.c @@ -279,6 +279,18 @@ static int cros_ec_host_command_proto_query(struct cros_ec_device *ec_dev, msg->insize = sizeof(struct ec_response_get_protocol_info);

ret = send_command(ec_dev, msg); + /* + * Send command once again when timeout occurred. + * Fingerprint MCU (FPMCU) is restarted during system boot which + * introduces small window in which FPMCU won't respond for any + * messages sent by kernel. There is no need to wait before next + * attempt because we waited at least EC_MSG_DEADLINE_MS. + */ + if (ret == -ETIMEDOUT) { + dev_warn(ec_dev->dev, + "Timeout to get response from EC. Retrying.\n"); + ret = send_command(ec_dev, msg); + }

if (ret < 0) { dev_dbg(ec_dev->dev,