linux-kernel - [PATCH v5] bus: mhi: host: Avoid ringing EV DB if there is no elements to process

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Message-Id: <1677087470-7004-1-git-send-email-quic_vpernami@quicinc.com>
Date:   Wed, 22 Feb 2023 23:07:48 +0530
From:   Vivek Pernamitta <quic_vpernami@...cinc.com>
To:     mhi@...ts.linux.dev
Cc:     quic_qianyu@...cinc.com, manivannan.sadhasivam@...aro.org,
        quic_vbadigan@...cinc.com, quic_krichai@...cinc.com,
        quic_skananth@...cinc.com, mrana@...cinc.com,
        Vivek Pernamitta <quic_vpernami@...cinc.com>,
        Manivannan Sadhasivam <mani@...nel.org>,
        Alex Elder <elder@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jeffrey Hugo <quic_jhugo@...cinc.com>,
        Hemant Kumar <hemantk@...eaurora.org>,
        Bhaumik Bhatt <bbhatt@...eaurora.org>,
        linux-arm-msm@...r.kernel.org (open list:MHI BUS),
        linux-kernel@...r.kernel.org (open list)
Subject: [PATCH v5] bus: mhi: host: Avoid ringing EV 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. This could cause
doorbell event to be processed by MHI device to check for
any ring elements even it is none and also it will occupy
lot of bandwidth on peripheral when mhi_poll() is called in
aggressive loop.

Signed-off-by: Vivek Pernamitta <quic_vpernami@...cinc.com>
Reviewed-by: Jeffrey Hugo <quic_jhugo@...cinc.com>

---
changes since v4:
	updating the commit text with more information.
changes since v3:
	- Updating commit text for multiple versions of patches.
changes since v2:
	- Updated comments in code.
changes since v1:
	- Add an check to avoid ringing EV DB in mhi_process_ctrl_ev_ring().
---
 drivers/bus/mhi/host/main.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/bus/mhi/host/main.c b/drivers/bus/mhi/host/main.c
index df0fbfe..1bbdb75 100644
--- a/drivers/bus/mhi/host/main.c
+++ b/drivers/bus/mhi/host/main.c
@@ -961,7 +961,9 @@ int mhi_process_ctrl_ev_ring(struct mhi_controller *mhi_cntrl,
 	}
 
 	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);
 
@@ -1031,7 +1033,9 @@ 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);
 
-- 
2.7.4