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From:   Vivek Pernamitta <quic_vpernami@quicinc.com>
To:     mhi@lists.linux.dev
Cc:     quic_qianyu@quicinc.com, manivannan.sadhasivam@linaro.org,
        quic_vbadigan@quicinc.com, quic_krichai@quicinc.com,
        quic_skananth@quicinc.com,
        Vivek Pernamitta <quic_vpernami@quicinc.com>,
        Manivannan Sadhasivam <mani@kernel.org>,
        Jeffrey Hugo <quic_jhugo@quicinc.com>,
        Bhaumik Bhatt <bbhatt@codeaurora.org>,
        Hemant Kumar <hemantk@codeaurora.org>,
        linux-arm-msm@vger.kernel.org (open list:MHI BUS),
        linux-kernel@vger.kernel.org (open list)
Subject: [PATCH V5] bus: mhi: host: Avoid ringing EV DB if there is no elements to process
Date:   Tue,  4 Apr 2023 15:11:10 +0530
Message-Id: <1680601272-8795-1-git-send-email-quic_vpernami@quicinc.com>
Precedence: bulk

curenlty mhi_process_data_event_ring()/mhi_process_ctrl_ev_ring()
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.
So ring event DB only if any event ring elements are processed.

Signed-off-by: Vivek Pernamitta <quic_vpernami@quicinc.com>
Reviewed-by: Jeffrey Hugo <quic_jhugo@quicinc.com>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
---
changes since v5:
	updating the commit text.
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