linux-kernel - Re: [PATCH V1] bus: mhi: host: Avoid ringing EV DB if there is no elements to process

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Message-ID: <0e630740-6913-0fb0-3ba1-1afc0aa61669@quicinc.com>
Date:   Tue, 21 Feb 2023 08:52:57 -0700
From:   Jeffrey Hugo <quic_jhugo@...cinc.com>
To:     Vivek Pernamitta <quic_vpernami@...cinc.com>, <mhi@...ts.linux.dev>
CC:     <quic_qianyu@...cinc.com>, <manivannan.sadhasivam@...aro.org>,
        "Manivannan Sadhasivam" <mani@...nel.org>,
        Alex Elder <elder@...aro.org>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        Hemant Kumar <hemantk@...eaurora.org>,
        Bhaumik Bhatt <bbhatt@...eaurora.org>,
        Paul Davey <paul.davey@...iedtelesis.co.nz>,
        "open list:MHI BUS" <linux-arm-msm@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V1] bus: mhi: host: Avoid ringing EV DB if there is no
 elements to process

On 2/21/2023 3:15 AM, Vivek Pernamitta wrote:
> Avoid ringing Event DB if there is no elements to process.
> As mhi_poll function can be called by mhi client drivers
> which will call process_event, which will ring DB even if
> there no ring elements to process.
> 
> Signed-off-by: Vivek Pernamitta <quic_vpernami@...cinc.com>
> ---
>   drivers/bus/mhi/host/main.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/bus/mhi/host/main.c b/drivers/bus/mhi/host/main.c
> index df0fbfe..8bf8394 100644
> --- a/drivers/bus/mhi/host/main.c
> +++ b/drivers/bus/mhi/host/main.c
> @@ -1031,7 +1031,9 @@ int mhi_process_data_event_ring(struct mhi_controller *mhi_cntrl,
>   		count++;
>   	}
>   	read_lock_bh(&mhi_cntrl->pm_lock);
> -	if (likely(MHI_DB_ACCESS_VALID(mhi_cntrl)))
> +
> +	/* Ring EV DB only if there is any pending element to process */
> +	if (likely(MHI_DB_ACCESS_VALID(mhi_cntrl)) && count)
>   		mhi_ring_er_db(mhi_event);
>   	read_unlock_bh(&mhi_cntrl->pm_lock);
>   

Seems like this optimization also applies to mhi_process_ctrl_ev_ring(). 
  Why not update that as well?