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Subject[PATCH v3] usb: typec: ucsi: Wait 20ms before reading CCI after a reset
The PPM might take time to process a reset. Allow 20ms for the reset to
be processed before reading the CCI.

This should not slow down existing implementations because they would
not set any bits in the CCI after a reset, and would take a 20ms delay
to read the CCI anyway. This change makes the delay explicit, and
reduces a CCI read. Based on the spec, the PPM has 10ms to set busy, so,
20ms seems like a reasonable delay before we read the CCI.

Signed-off-by: Pavan Holla <pholla@chromium.org>
Reviewed-by: Prashant Malani <pmalani@chromium.org>
---
The PPM might take time to process a reset and set the CCI. Give the PPM
20ms to update it's CCI.

Commit message now summarizes discussion in v1.
---
Changes in v3:
- Commit message updated.
- Link to v2: https://lore.kernel.org/r/20240403-ucsi-reset-delay-v2-1-244c175825a4@chromium.org

Changes in v2:
- Commit message updated.
- Link to v1: https://lore.kernel.org/r/20240325-ucsi-reset-delay-v1-1-d9e183e0f1e6@chromium.org
---
drivers/usb/typec/ucsi/ucsi.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/typec/ucsi/ucsi.c b/drivers/usb/typec/ucsi/ucsi.c
index cf52cb34d285..c0706c40fa64 100644
--- a/drivers/usb/typec/ucsi/ucsi.c
+++ b/drivers/usb/typec/ucsi/ucsi.c
@@ -1280,6 +1280,9 @@ static int ucsi_reset_ppm(struct ucsi *ucsi)
goto out;
}

+ /* Give the PPM time to process a reset before reading CCI */
+ msleep(20);
+
ret = ucsi->ops->read(ucsi, UCSI_CCI, &cci, sizeof(cci));
if (ret)
goto out;
@@ -1293,7 +1296,6 @@ static int ucsi_reset_ppm(struct ucsi *ucsi)
goto out;
}

- msleep(20);
} while (!(cci & UCSI_CCI_RESET_COMPLETE));

out:
---
base-commit: 4cece764965020c22cff7665b18a012006359095
change-id: 20240325-ucsi-reset-delay-bdf6712455fd
Best regards,
--
Pavan Holla <pholla@chromium.org>


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