2023-02-22 11:44:53

by Vivek Pernamitta

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 <[email protected]>

---
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

2023-02-22 15:43:45

by Jeffrey Hugo

Subject: Re: [PATCH v4] bus: mhi: host: Avoid ringing EV DB if there is no elements to process

On 2/22/2023 4:43 AM, Vivek Pernamitta wrote:
> Avoid ringing Event DB if there is no elements to process.

This is almost exactly identical to $SUBJECT and therefore redundant.

> 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.

I think that you could be more clear on why this is a problem that
should be addressed. Perhaps add a sentence like "These doorbell events
needlessly interrupt the MHI device to checked for ring elements when
there are none."

With the commit text updated, you can add
Reviewed-by: Jeffrey Hugo <[email protected]>

>
> Signed-off-by: Vivek Pernamitta <[email protected]>
>
> ---
> 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);
>