linux-kernel - [PATCH v4] bus: mhi: host: Avoid ringing EV DB if there is no elements to process

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Message-Id: <1677066231-14931-1-git-send-email-quic_vpernami@quicinc.com>
Date:   Wed, 22 Feb 2023 17:13:49 +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,
        Vivek Pernamitta <quic_vpernami@...cinc.com>,
        Manivannan Sadhasivam <mani@...nel.org>,
        Alex Elder <elder@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Hemant Kumar <hemantk@...eaurora.org>,
        Jeffrey Hugo <quic_jhugo@...cinc.com>,
        Paul Davey <paul.davey@...iedtelesis.co.nz>,
        linux-arm-msm@...r.kernel.org (open list:MHI BUS),
        linux-kernel@...r.kernel.org (open list)
Subject: [PATCH v4] bus: mhi: host: Avoid ringing EV DB if there is no elements to process

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>

---
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