linux-kernel - Re: [PATCH v3 4/7] bus: mhi: core: Add support to stop or start channel data transfers

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Date:   Thu, 03 Dec 2020 17:44:28 -0800
From:   Bhaumik Bhatt <bbhatt@...eaurora.org>
To:     Hemant Kumar <hemantk@...eaurora.org>
Cc:     manivannan.sadhasivam@...aro.org, linux-arm-msm@...r.kernel.org,
        loic.poulain@...aro.org, jhugo@...eaurora.org,
        linux-kernel@...r.kernel.org, hemantk=codeaurora.org@...eaurora.org
Subject: Re: [PATCH v3 4/7] bus: mhi: core: Add support to stop or start
 channel data transfers

On 2020-12-02 04:33 PM, Hemant Kumar wrote:
> Hi Bhaumik,
> 
> On 12/2/20 3:40 PM, Bhaumik Bhatt wrote:
>> Some MHI client drivers may want to request a pause or halt of
>> data transfer activity on their channels. Support for this does
>> not exist and must be introduced, wherein the channel context is
>> not reset or cleared but only the STOP channel command is issued.
>> This would need to be paired with an API that allows resuming the
>> data transfer activity on channels by use of the START channel
>> command. This API assumes that the context information is already
> 
> is it a better option to make sure channel context is setup as this is
> an exported API. Hence check for channel context bail out in case
> channel context is not setup with an err msg ?
> 
This is a better method, yes. Addressed in v4.
>> setup. Enable this using two new APIs, mhi_start_transfer() and
>> mhi_stop_transfer().
>> 
>> Signed-off-by: Bhaumik Bhatt <bbhatt@...eaurora.org>
>> ---
>>   drivers/bus/mhi/core/main.c | 41 
>> +++++++++++++++++++++++++++++++++++++++++
>>   include/linux/mhi.h         | 19 +++++++++++++++++++
>>   2 files changed, 60 insertions(+)
>> 
>> diff --git a/drivers/bus/mhi/core/main.c b/drivers/bus/mhi/core/main.c
>> index 4cc5ced..2e4b34a 100644
>> --- a/drivers/bus/mhi/core/main.c
>> +++ b/drivers/bus/mhi/core/main.c
>> @@ -1552,6 +1552,47 @@ void mhi_unprepare_from_transfer(struct 
>> mhi_device *mhi_dev)
>>   }
>>   EXPORT_SYMBOL_GPL(mhi_unprepare_from_transfer);
>>   +static int mhi_update_transfer_state(struct mhi_device *mhi_dev,
>> +				     enum mhi_ch_state_type to_state)
>> +{
>> +	struct mhi_controller *mhi_cntrl = mhi_dev->mhi_cntrl;
>> +	struct mhi_chan *mhi_chan;
>> +	int dir, ret;
>> +
>> +	for (dir = 0; dir < 2; dir++) {
>> +		mhi_chan = dir ? mhi_dev->ul_chan : mhi_dev->dl_chan;
>> +
>> +		if (!mhi_chan)
>> +			continue;
>> +
>> +		/*
>> +		 * Bail out if one of the channels fail as client will reset
>> +		 * both upon failure
>> +		 */
>> +		mutex_lock(&mhi_chan->mutex);
>> +		ret = mhi_update_channel_state(mhi_cntrl, mhi_chan, to_state);
>> +		if (ret) {
>> +			mutex_unlock(&mhi_chan->mutex);
>> +			return ret;
>> +		}
>> +		mutex_unlock(&mhi_chan->mutex);
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>> +int mhi_stop_transfer(struct mhi_device *mhi_dev)
>> +{
>> +	return mhi_update_transfer_state(mhi_dev, MHI_CH_STATE_TYPE_STOP);
>> +}
>> +EXPORT_SYMBOL_GPL(mhi_stop_transfer);
>> +
>> +int mhi_start_transfer(struct mhi_device *mhi_dev)
>> +{
>> +	return mhi_update_transfer_state(mhi_dev, MHI_CH_STATE_TYPE_START);
>> +}
>> +EXPORT_SYMBOL_GPL(mhi_start_transfer);
>> +
>>   int mhi_poll(struct mhi_device *mhi_dev, u32 budget)
>>   {
>>   	struct mhi_controller *mhi_cntrl = mhi_dev->mhi_cntrl;
>> diff --git a/include/linux/mhi.h b/include/linux/mhi.h
>> index aa9757e..35779a0 100644
>> --- a/include/linux/mhi.h
>> +++ b/include/linux/mhi.h
>> @@ -704,6 +704,25 @@ int mhi_prepare_for_transfer(struct mhi_device 
>> *mhi_dev);
>>   void mhi_unprepare_from_transfer(struct mhi_device *mhi_dev);
>>     /**
>> + * mhi_stop_transfer - Pauses ongoing channel activity by issuing the 
>> STOP
>> + *                     channel command to both UL and DL channels. 
>> This command
>> + *                     does not reset the channel context and the 
>> client drivers
>> + *                     can issue mhi_start_transfer to resume 
>> activity.
>> + * @mhi_dev: Device associated with the channels
>> + */
>> +int mhi_stop_transfer(struct mhi_device *mhi_dev);
>> +
>> +/**
>> + * mhi_start_transfer - Resumes channel activity by issuing the START 
>> channel
>> + *                      command to both UL and DL channels. This 
>> command assumes
>> + *                      the channel context is already setup and the 
>> client
>> + *                      drivers can issue mhi_stop_transfer to pause 
>> activity if
>> + *                      required.
>> + * @mhi_dev: Device associated with the channels
>> + */
>> +int mhi_start_transfer(struct mhi_device *mhi_dev);
>> +
>> +/**
>>    * mhi_poll - Poll for any available data in DL direction
>>    * @mhi_dev: Device associated with the channels
>>    * @budget: # of events to process
>> 
> Overall change looks good.
> 
> Thanks,
> Hemant

Thanks,
Bhaumik
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