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

[Bhaumik Bhatt]

On 2021-02-19 06:55 AM, Jeffrey Hugo wrote:
> On 2/18/2021 7:18 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 | 32 ++++++++++++++++----------------
> >   1 file changed, 16 insertions(+), 16 deletions(-)
> >
> > diff --git a/drivers/bus/mhi/core/pm.c b/drivers/bus/mhi/core/pm.c
> > index 65ebca8..ec0060c 100644
> > --- a/drivers/bus/mhi/core/pm.c
> > +++ b/drivers/bus/mhi/core/pm.c
> > @@ -9,6 +9,7 @@
> >   #include <linux/dma-direction.h>
> >   #include <linux/dma-mapping.h>
> >   #include <linux/interrupt.h>
> > +#include <linux/iopoll.h>
> >   #include <linux/list.h>
> >   #include <linux/mhi.h>
> >   #include <linux/module.h>
> > @@ -157,30 +158,29 @@ int mhi_ready_state_transition(struct 
> > mhi_controller *mhi_cntrl)
> >   	struct mhi_event *mhi_event;
> >   	enum mhi_pm_state cur_state;
> >   	struct device *dev = &mhi_cntrl->mhi_dev->dev;
> > -	u32 reset = 1, ready = 0;
> > +	u32 reset, ready;
> >   	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 = readl_relaxed_poll_timeout(base + MHICTRL, reset,
> > +					 !(reset & MHICTRL_RESET_MASK), 25000,
> > +					 mhi_cntrl->timeout_ms * 1000);
> > +	if (ret) {
> > +		dev_err(dev, "Device failed to clear MHI Reset\n");
> > +		return -ETIMEDOUT;
> > +	}
> > +
> > +	ret = readl_relaxed_poll_timeout(base + MHISTATUS, ready,
> > +					 (ready & MHISTATUS_READY_MASK), 25000,
> > +					 mhi_cntrl->timeout_ms * 1000);
> > +	if (ret) {
> > +		dev_err(dev, "Device failed to enter MHI Ready\n");
> >   		return -ETIMEDOUT;
> >   	}
>
> I think this gets a NACK from me.
>
> mhi_read_reg_field() uses the controller defined accessor method
> read_reg().  readl_relaxed_poll_timeout() does not.  If, say, MHI was
> implemented over I2C, direct readl() accesses wouldn't be valid, and
> this would break.
>
> Also, if the link ever goes down in the middle if the timeout, the
> controller read_reg() should detect that, but
> readl_relaxed_poll_timeout() would not.
>
> I'm fine with this concept, but I think the implementation needs to be 
> adjusted.
I agree. I will think on this and plan it around the controller defined 
method.

Thanks,
Bhaumik
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