On Mon, Nov 04, 2024 at 03:42:52PM +0000, Łukasz Bartosik wrote:
> OPM PPM LPM
> | 1.send cmd | |
> |-------------------------->| |
> | |-- |
> | | | 2.set busy bit in CCI |
> | |<- |
> | 3.notify the OPM | |
> |<--------------------------| |
> | | 4.send cmd to be executed |
> | |-------------------------->|
> | | |
> | | 5.cmd completed |
> | |<--------------------------|
> | | |
> | |-- |
> | | | 6.set cmd completed |
> | |<- bit in CCI |
> | | |
> | 7.handle notification | |
> | from point 3, read CCI | |
> |<--------------------------| |
> | | |
> | 8.notify the OPM | |
> |<--------------------------| |
> | | |
>
> When the PPM receives command from the OPM (p.1) it sets the busy bit
> in the CCI (p.2), sends notification to the OPM (p.3) and forwards the
> command to be executed by the LPM (p.4). When the PPM receives command
> completion from the LPM (p.5) it sets command completion bit in the CCI
> (p.6) and sends notification to the OPM (p.8). If command execution by
> the LPM is fast enough then when the OPM starts handling the notification
> from p.3 in p.7 and reads the CCI value it will see command completion bit
> and will call complete(). Then complete() might be called again when the
> OPM handles notification from p.8.
I think the change is fine, but I'd like to understand, what code path
causes the first read from the OPM side before the notification from
the PPM?
>
> This fix replaces test_bit() with test_and_clear_bit()
> in ucsi_notify_common() in order to call complete() only
> once per request.
>
> Fixes: 584e8df58942 ("usb: typec: ucsi: extract common code for command handling")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Łukasz Bartosik <ukaszb@xxxxxxxxxxxx>
> ---
> drivers/usb/typec/ucsi/ucsi.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/usb/typec/ucsi/ucsi.c b/drivers/usb/typec/ucsi/ucsi.c
> index e0f3925e401b..7a9b987ea80c 100644
> --- a/drivers/usb/typec/ucsi/ucsi.c
> +++ b/drivers/usb/typec/ucsi/ucsi.c
> @@ -46,11 +46,11 @@ void ucsi_notify_common(struct ucsi *ucsi, u32 cci)
> ucsi_connector_change(ucsi, UCSI_CCI_CONNECTOR(cci));
>
> if (cci & UCSI_CCI_ACK_COMPLETE &&
> - test_bit(ACK_PENDING, &ucsi->flags))
> + test_and_clear_bit(ACK_PENDING, &ucsi->flags))
> complete(&ucsi->complete);
>
> if (cci & UCSI_CCI_COMMAND_COMPLETE &&
> - test_bit(COMMAND_PENDING, &ucsi->flags))
> + test_and_clear_bit(COMMAND_PENDING, &ucsi->flags))
> complete(&ucsi->complete);
> }
> EXPORT_SYMBOL_GPL(ucsi_notify_common);
> --
> 2.47.0.199.ga7371fff76-goog
>
--
With best wishes
Dmitry
