Re: [PATCH 1/3] bus: mhi: core: Handle syserr during power_up

[Jeffrey Hugo]

On 4/7/2020 12:26 AM, Manivannan Sadhasivam wrote:
> On Mon, Apr 06, 2020 at 03:04:35PM -0600, Jeffrey Hugo wrote:
> > The MHI device may be in the syserr state when we attempt to init it in
> > power_up().  Since we have no local state, the handling is simple -
> > reset the device and wait for it to transition out of the reset state.
> >
> > Signed-off-by: Jeffrey Hugo <jhugo@xxxxxxxxxxxxxx>
> > ---
> >   drivers/bus/mhi/core/pm.c | 20 ++++++++++++++++++++
> >   1 file changed, 20 insertions(+)
> >
> > diff --git a/drivers/bus/mhi/core/pm.c b/drivers/bus/mhi/core/pm.c
> > index 52690cb..cd6ba23 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>
> > @@ -760,6 +761,7 @@ static void mhi_deassert_dev_wake(struct mhi_controller *mhi_cntrl,
> >   
> >   int mhi_async_power_up(struct mhi_controller *mhi_cntrl)
> >   {
> > +	enum mhi_state state;
> >   	enum mhi_ee_type current_ee;
> >   	enum dev_st_transition next_state;
> >   	struct device *dev = &mhi_cntrl->mhi_dev->dev;
> > @@ -829,6 +831,24 @@ int mhi_async_power_up(struct mhi_controller *mhi_cntrl)
> >   		goto error_bhi_offset;
> >   	}
> >   
> > +	state = mhi_get_mhi_state(mhi_cntrl);
> > +	if (state == MHI_STATE_SYS_ERR) {
> > +		mhi_set_mhi_state(mhi_cntrl, MHI_STATE_RESET);
> > +		ret = readl_poll_timeout(mhi_cntrl->regs + MHICTRL, val,
> > +					 !(val & MHICTRL_RESET_MASK), 1000,
>
> Hmm. Do we really need a max 1ms delay between each read? I'd prefer to have
> 100ns to reduce the wait time.


I assume you mean 100us since that's the units of the parameter, and 
usleep_range is the actual delay mechanism.  Please correct me if that 
is a bad assumption.

I chose 1ms to try to avoid flooding the bus, since on one system we 
care about, the round trip time was observed to be ~1ms.  However, that 
is fairly arbitrary, so a factor of 10 reduction don't seem like a 
significant issue.

> > +					 mhi_cntrl->timeout_ms * 1000);
> > +		if (ret) {
> > +			dev_info(dev, "Failed to reset syserr\n");
>
> dev_info(dev, "Failed to reset MHI due to syserr state\n"); ?

Ah yes, that is clearer.  Thanks

--
Jeffrey Hugo
Qualcomm Technologies, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.