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

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Date:   Wed, 2 Dec 2020 16:33:00 -0800
From:   Hemant Kumar <hemantk@...eaurora.org>
To:     Bhaumik Bhatt <bbhatt@...eaurora.org>,
        manivannan.sadhasivam@...aro.org
Cc:     linux-arm-msm@...r.kernel.org, loic.poulain@...aro.org,
        jhugo@...eaurora.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 4/7] bus: mhi: core: Add support to stop or start
 channel data transfers

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 ?

> 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
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