linux-kernel - Re: [PATCH v1 5/5] bus: mhi: core: Handle write lock properly in mhi_pm_m0

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Date:   Tue, 12 May 2020 12:27:15 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Hemant Kumar <hemantk@...eaurora.org>
Cc:     linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        jhugo@...eaurora.org, bbhatt@...eaurora.org
Subject: Re: [PATCH v1 5/5] bus: mhi: core: Handle write lock properly in
 mhi_pm_m0_transition

On Mon, May 11, 2020 at 07:03:09PM -0700, Hemant Kumar wrote:
> Take write lock only to protect db_mode member of mhi channel.
> This allows rest of the mhi channels to just take read lock which
> fine grains the locking. It prevents channel readers to starve if
> they try to enter critical section after a writer.
> 
> Signed-off-by: Hemant Kumar <hemantk@...eaurora.org>

Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>

Thanks,
Mani

> ---
>  drivers/bus/mhi/core/pm.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/bus/mhi/core/pm.c b/drivers/bus/mhi/core/pm.c
> index 345f197..de5abb2 100644
> --- a/drivers/bus/mhi/core/pm.c
> +++ b/drivers/bus/mhi/core/pm.c
> @@ -288,14 +288,18 @@ int mhi_pm_m0_transition(struct mhi_controller *mhi_cntrl)
>  	for (i = 0; i < mhi_cntrl->max_chan; i++, mhi_chan++) {
>  		struct mhi_ring *tre_ring = &mhi_chan->tre_ring;
>  
> -		write_lock_irq(&mhi_chan->lock);
> -		if (mhi_chan->db_cfg.reset_req)
> +		if (mhi_chan->db_cfg.reset_req) {
> +			write_lock_irq(&mhi_chan->lock);
>  			mhi_chan->db_cfg.db_mode = true;
> +			write_unlock_irq(&mhi_chan->lock);
> +		}
> +
> +		read_lock_irq(&mhi_chan->lock);
>  
>  		/* Only ring DB if ring is not empty */
>  		if (tre_ring->base && tre_ring->wp  != tre_ring->rp)
>  			mhi_ring_chan_db(mhi_cntrl, mhi_chan);
> -		write_unlock_irq(&mhi_chan->lock);
> +		read_unlock_irq(&mhi_chan->lock);
>  	}
>  
>  	mhi_cntrl->wake_put(mhi_cntrl, false);
> -- 
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> a Linux Foundation Collaborative Project