Re: [PATCH v3 9/9] bus: mhi: ep: wake up host is the MHI state is in M3

[Bjorn Helgaas <helgaas@kernel.org>]

On Fri, Jul 07, 2023 at 02:41:57PM +0300, Dan Carpenter wrote:
> On Fri, Jul 07, 2023 at 04:33:56PM +0530, Krishna chaitanya chundru wrote:
> > If the MHI state is in M3 then the most probably the host kept the
> > device in D3 hot or D3 cold, due to that endpoint transctions will not
> > be read by the host, so endpoint wakes up host to bring the host to D0
> > which eventually bring back the MHI state to M0.
> > 
> > Signed-off-by: Krishna chaitanya chundru <quic_krichai@quicinc.com>
> > ---
> >  drivers/bus/mhi/ep/main.c | 28 ++++++++++++++++++++++++++++
> >  1 file changed, 28 insertions(+)
> > 
> > diff --git a/drivers/bus/mhi/ep/main.c b/drivers/bus/mhi/ep/main.c
> > index 6008818..46a8a3c 100644
> > --- a/drivers/bus/mhi/ep/main.c
> > +++ b/drivers/bus/mhi/ep/main.c
> > @@ -25,6 +25,27 @@ static DEFINE_IDA(mhi_ep_cntrl_ida);
> >  static int mhi_ep_create_device(struct mhi_ep_cntrl *mhi_cntrl, u32 ch_id);
> >  static int mhi_ep_destroy_device(struct device *dev, void *data);
> >  
> > +static bool mhi_ep_wake_host(struct mhi_ep_cntrl *mhi_cntrl)
> > +{
> > +	enum mhi_state state;
> > +	bool mhi_reset;
> > +	u32 count = 0;
> > +
> > +	mhi_cntrl->wakeup_host(mhi_cntrl);
> > +
> > +	/* Wait for Host to set the M0 state */
> > +	do {
> > +		msleep(M0_WAIT_DELAY_MS);
> > +		mhi_ep_mmio_get_mhi_state(mhi_cntrl, &state, &mhi_reset);
> > +		count++;
> > +	} while (state != MHI_STATE_M0 && count < M0_WAIT_COUNT);
> > +
> >+	if (state != MHI_STATE_M0)
> >+		return false;
> 
> Functions which return false on success are an abomination.  Also
> boolean functions should be named for the question they answer such
> as access_ok() or has_feature() etc.

+1.  Also nice if boolean functions do not have side effects, so in
this case, where mhi_ep_wake_host() *does* something that might fail,
I think "return 0 for success or negative error value" is easier to
read.

> Write it like this:
> 
> static int mhi_ep_wake_host(struct mhi_ep_cntrl *mhi_cntrl)
> {
> 	enum mhi_state state;
> 	bool mhi_reset;
> 	int count = 0;
> 
> 	mhi_cntrl->wakeup_host(mhi_cntrl);
> 
> 	while (count++ < M0_WAIT_COUNT) {
> 		msleep(M0_WAIT_DELAY_MS);
> 
> 		mhi_ep_mmio_get_mhi_state(mhi_cntrl, &state, &mhi_reset);
> 		if (state == MHI_STATE_M0)
> 			return 0;
> 	}
> 	return -ENODEV;
> }