Re: [PATCH v3 2/3] bus: mhi: core: Move to polling method to wait for MHI ready

[Bhaumik Bhatt <bbhatt@xxxxxxxxxxxxxx>]

On 2021-03-10 11:02 AM, Jeffrey Hugo wrote:
> On 2/23/2021 8:44 PM, Bhaumik Bhatt wrote:
> > In certain devices, it is likely that there is no incoming MHI
> > interrupt for a transition to MHI READY state. One such example
> > is the move from Pass Through to an SBL or AMSS execution
> > environment. In order to facilitate faster bootup times as there
> > is no need to wait until timeout_ms completes, MHI host can poll
> > every 25 milliseconds to check if device has entered MHI READY
> > until a maximum timeout of twice the timeout_ms is reached.
> >
> > Signed-off-by: Bhaumik Bhatt <bbhatt@xxxxxxxxxxxxxx>
> > ---
> >   drivers/bus/mhi/core/pm.c | 31 ++++++++++++++-----------------
> >   1 file changed, 14 insertions(+), 17 deletions(-)
> >
> > diff --git a/drivers/bus/mhi/core/pm.c b/drivers/bus/mhi/core/pm.c
> > index 681960c..5fe33d4 100644
> > --- a/drivers/bus/mhi/core/pm.c
> > +++ b/drivers/bus/mhi/core/pm.c
> > @@ -153,34 +153,31 @@ static void mhi_toggle_dev_wake(struct 
> > mhi_controller *mhi_cntrl)
> >   /* Handle device ready state transition */
> >   int mhi_ready_state_transition(struct mhi_controller *mhi_cntrl)
> >   {
> > -	void __iomem *base = mhi_cntrl->regs;
> >   	struct mhi_event *mhi_event;
> >   	enum mhi_pm_state cur_state;
> >   	struct device *dev = &mhi_cntrl->mhi_dev->dev;
> > -	u32 reset = 1, ready = 0;
> >   	int ret, i;
> >   -	/* Wait for RESET to be cleared and READY bit to be set by the 
> > device */
> > -	wait_event_timeout(mhi_cntrl->state_event,
> > -			   MHI_PM_IN_FATAL_STATE(mhi_cntrl->pm_state) ||
> > -			   mhi_read_reg_field(mhi_cntrl, base, MHICTRL,
> > -					      MHICTRL_RESET_MASK,
> > -					      MHICTRL_RESET_SHIFT, &reset) ||
> > -			   mhi_read_reg_field(mhi_cntrl, base, MHISTATUS,
> > -					      MHISTATUS_READY_MASK,
> > -					      MHISTATUS_READY_SHIFT, &ready) ||
> > -			   (!reset && ready),
> > -			   msecs_to_jiffies(mhi_cntrl->timeout_ms));
> > -
> >   	/* Check if device entered error state */
> >   	if (MHI_PM_IN_FATAL_STATE(mhi_cntrl->pm_state)) {
> >   		dev_err(dev, "Device link is not accessible\n");
> >   		return -EIO;
> >   	}
> >   -	/* Timeout if device did not transition to ready state */
> > -	if (reset || !ready) {
> > -		dev_err(dev, "Device Ready timeout\n");
> > +	/* Wait for RESET to be cleared and READY bit to be set by the 
> > device */
> > +	ret = mhi_poll_reg_field(mhi_cntrl, mhi_cntrl->regs, MHICTRL,
> > +				 MHICTRL_RESET_MASK, MHICTRL_RESET_SHIFT, 0,
> > +				 25000);
> > +	if (ret) {
> > +		dev_err(dev, "Device failed to clear MHI Reset\n");
> > +		return -ETIMEDOUT;
> > +	}
> > +
> > +	ret = mhi_poll_reg_field(mhi_cntrl, mhi_cntrl->regs, MHISTATUS,
> > +				 MHISTATUS_READY_MASK, MHISTATUS_READY_SHIFT, 1,
> > +				 25000);
>
> You use the magic number "25000" twice here.  Its my understanding
> that the preference is to inline a magic number if its used in one
> spot, but use a macro if its used more than that.
>
> Both uses are confined to this function, and in close proximity, so
> chances that one gets updated without the other seem minimal, so this
> feels like a borderline case.  I don't know if Mani has an opinion
> here.
>
> I'd probably err on the side of making a macro or a single variable.
> If not, I think some comments explaining the value are warranted
> (should comment the macro as well).
I think just using a variable would be good enough here. I can add a 
comment
when defining the interval variable.
> > +	if (ret) {
> > +		dev_err(dev, "Device failed to enter MHI Ready\n");
> >   		return -ETIMEDOUT;
> >   	}

Thanks,
Bhaumik
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