linux-kernel - Re: [PATCH 1/3] bus: mhi: core: Handle syserr during power

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Message-ID: <f63b0a23-97d3-e690-70ae-a4485d42b28f@codeaurora.org>
Date:   Tue, 7 Apr 2020 09:11:33 -0600
From:   Jeffrey Hugo <jhugo@...eaurora.org>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc:     hemantk@...eaurora.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] bus: mhi: core: Handle syserr during power_up

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@...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..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.