On Mon, Nov 18, 2024 at 6:58 PM Dmitry Baryshkov
<dmitry.baryshkov@xxxxxxxxxx> wrote:
>
> 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?
>
The read from the OPM in p.7 is a result of notification in p.3 but I agree
it is misleading since you pointed it out. I will reorder p.7 and p.8.
Thanks,
Lukasz
> >
> > 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
