linux-kernel - Re: [PATCH v3 1/3] bus: mhi: core: Introduce internal register poll helper function

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Date:   Wed, 10 Mar 2021 14:56:59 -0800
From:   Bhaumik Bhatt <bbhatt@...eaurora.org>
To:     Jeffrey Hugo <jhugo@...eaurora.org>
Cc:     manivannan.sadhasivam@...aro.org, linux-arm-msm@...r.kernel.org,
        hemantk@...eaurora.org, linux-kernel@...r.kernel.org,
        loic.poulain@...aro.org, carl.yin@...ctel.com,
        naveen.kumar@...ctel.com, jhugo=codeaurora.org@...eaurora.org
Subject: Re: [PATCH v3 1/3] bus: mhi: core: Introduce internal register poll
 helper function

On 2021-03-10 10:57 AM, Jeffrey Hugo wrote:
> On 2/23/2021 8:44 PM, 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..249ae26 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 = -ENOENT;
Make this 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 -EIO;
> 
> I generally dislike recoding return codes.  Do you believe it adds
> value here?  I'm concerned that if I'm debugging an error, I'll get
> EIO, which I trace to here, but then I don't know what the actual
> error from mhi_read_reg_field() was.
> 
Thanks for pointing out. I don't think its necessary to recode and I can 
go back
to returning whatever the reg_field API returns. I have added the 
proposed changes
here which help fix a potential bug that we'd return 0 if read is 
successful but
polling fails.
>> +
>> +		if (out == val)
>> +			return 0;
>> +
>> +		udelay(delayus);
>> +	}
>> +
>> +	return ret;
return -ENOENT; to signify failure to find the entry after poll duration 
completes
>> +}
>> +
>>   void mhi_write_reg(struct mhi_controller *mhi_cntrl, void __iomem 
>> *base,
>>   		   u32 offset, u32 val)
>>   {
>> 

Thanks,
Bhaumik
---
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