linux-kernel - Re: [PATCH v2 1/5] bus: mhi: core: Handle syserr during power

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Message-ID: <11d9f35b-b911-7985-8846-0a45904ceed1@codeaurora.org>
Date:   Fri, 10 Apr 2020 09:03:08 -0600
From:   Jeffrey Hugo <jhugo@...eaurora.org>
To:     Hemant Kumar <hemantk@...eaurora.org>,
        manivannan.sadhasivam@...aro.org
Cc:     "linux-arm-msm@...r.kernel.org; bbhatt"@codeaurora.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/5] bus: mhi: core: Handle syserr during power_up

On 4/9/2020 6:55 PM, Hemant Kumar wrote:
> 
> On 4/7/20 9:50 AM, 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@...eaurora.org>
>> ---
>>   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..3285c9e 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,
>> +                     mhi_cntrl->timeout_ms * 1000);
> can we use this instead of polling because MSI is configures and int_vec 
> handler is registered
> 
>      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) || !reset ,
>                 msecs_to_jiffies(mhi_cntrl->timeout_ms));
> 
> 1) In case of MHI_PM_IN_FATAL_STATE we would not be accessing MHI reg
> 2) Consistent with current MHI driver code.

I'm not sure this works in the way you intend.

state_event is linked to the intvec, which is the BHI interrupt.  I 
don't see that the state_event is triggered in the MHI interrupt path 
(mhi_irq_handler).  So, if we are in the PBL EE, we would expect to see 
the BHI interrupt, but if we are in the AMSS EE, we would expect to see 
a MHI interrupt.

Now, for my concerned usecase, those two interrupts happen to be the 
same interrupt, so both will get triggered, but I don't expect that to 
be the same for all usecases.

So, with the solution I propose, we exit the wait (poll loop) as soon as 
we see the register change values.

With the solution you propose, if we only get the MHI interrupt, we'll 
have to wait out the entire timeout value, and then check the register. 
In this scenario, we are almost guaranteed to wait for longer than 
necessary.

Did I miss something?

>> +        if (ret) {
>> +            dev_info(dev, "Failed to reset MHI due to syserr state\n");
>> +            goto error_bhi_offset;
>> +        }
>> +
>> +        /*
>> +         * device cleares INTVEC as part of RESET processing,
>> +         * re-program it
>> +         */
>> +        mhi_write_reg(mhi_cntrl, mhi_cntrl->bhi, BHI_INTVEC, 0);
>> +    }
>> +
>>       /* Transition to next state */
>>       next_state = MHI_IN_PBL(current_ee) ?
>>           DEV_ST_TRANSITION_PBL : DEV_ST_TRANSITION_READY;
> 


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