linux-kernel - Re: [PATCH v5 1/2] bus: mhi: core: Introduce internal register poll helper function

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Date:   Wed, 31 Mar 2021 10:09:51 -0700
From:   Bhaumik Bhatt <bbhatt@...eaurora.org>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc:     linux-arm-msm@...r.kernel.org, hemantk@...eaurora.org,
        jhugo@...eaurora.org, linux-kernel@...r.kernel.org,
        carl.yin@...ctel.com, naveen.kumar@...ctel.com,
        loic.poulain@...aro.org
Subject: Re: [PATCH v5 1/2] bus: mhi: core: Introduce internal register poll
 helper function

Hi Mani,

On 2021-03-31 06:03 AM, Manivannan Sadhasivam wrote:
> On Mon, Mar 29, 2021 at 12:53:02PM -0700, Bhaumik Bhatt wrote:
>> Introduce helper function to allow MHI core driver to poll for
>> a value in a register field. This helps reach a common path to
>> read and poll register values along with a retry time interval.
>> 
>> Signed-off-by: Bhaumik Bhatt <bbhatt@...eaurora.org>
>> ---
>>  drivers/bus/mhi/core/internal.h |  3 +++
>>  drivers/bus/mhi/core/main.c     | 23 +++++++++++++++++++++++
>>  2 files changed, 26 insertions(+)
>> 
>> diff --git a/drivers/bus/mhi/core/internal.h 
>> b/drivers/bus/mhi/core/internal.h
>> index 6f80ec3..005286b 100644
>> --- a/drivers/bus/mhi/core/internal.h
>> +++ b/drivers/bus/mhi/core/internal.h
>> @@ -643,6 +643,9 @@ int __must_check mhi_read_reg(struct 
>> mhi_controller *mhi_cntrl,
>>  int __must_check mhi_read_reg_field(struct mhi_controller *mhi_cntrl,
>>  				    void __iomem *base, u32 offset, u32 mask,
>>  				    u32 shift, u32 *out);
>> +int __must_check mhi_poll_reg_field(struct mhi_controller *mhi_cntrl,
>> +				    void __iomem *base, u32 offset, u32 mask,
>> +				    u32 shift, u32 val, u32 delayus);
>>  void mhi_write_reg(struct mhi_controller *mhi_cntrl, void __iomem 
>> *base,
>>  		   u32 offset, u32 val);
>>  void mhi_write_reg_field(struct mhi_controller *mhi_cntrl, void 
>> __iomem *base,
>> diff --git a/drivers/bus/mhi/core/main.c b/drivers/bus/mhi/core/main.c
>> index 4e0131b..6f4b630 100644
>> --- a/drivers/bus/mhi/core/main.c
>> +++ b/drivers/bus/mhi/core/main.c
>> @@ -4,6 +4,7 @@
>>   *
>>   */
>> 
>> +#include <linux/delay.h>
>>  #include <linux/device.h>
>>  #include <linux/dma-direction.h>
>>  #include <linux/dma-mapping.h>
>> @@ -37,6 +38,28 @@ int __must_check mhi_read_reg_field(struct 
>> mhi_controller *mhi_cntrl,
>>  	return 0;
>>  }
>> 
>> +int __must_check mhi_poll_reg_field(struct mhi_controller *mhi_cntrl,
>> +				    void __iomem *base, u32 offset,
>> +				    u32 mask, u32 shift, u32 val, u32 delayus)
>> +{
>> +	int ret;
>> +	u32 out, retry = (mhi_cntrl->timeout_ms * 1000) / delayus;
>> +
>> +	while (retry--) {
>> +		ret = mhi_read_reg_field(mhi_cntrl, base, offset, mask, shift,
>> +					 &out);
>> +		if (ret)
>> +			return ret;
>> +
>> +		if (out == val)
>> +			return 0;
>> +
>> +		fsleep(delayus);
>> +	}
>> +
>> +	return -ENOENT;
> 
> Maybe I'm too late on this one, but I don't think -ENOENT is the 
> correct
> error code here. The error code will be returned only when the reg 
> field
> value didn't change as expected, so in that case it should be -EINVAL 
> or
> -ETIMEDOUT, no?
> 
> Thanks,
> Mani
> 

Thanks for pointing that out.

The intention of the error code was despite polling for whatever time 
period,
we were unable to see the value changing as expected. I think the 
-ETIMEDOUT
error code would be appropriate. Will upload a v6.

>> +}
>> +
>>  void mhi_write_reg(struct mhi_controller *mhi_cntrl, void __iomem 
>> *base,
>>  		   u32 offset, u32 val)
>>  {
>> --
>> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora 
>> Forum,
>> a Linux Foundation Collaborative Project
>> 

Thanks,
Bhaumik
---
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora 
Forum,
a Linux Foundation Collaborative Project