2020-05-12 02:05:23

by Hemant Kumar

Subject: [PATCH v1 5/5] bus: mhi: core: Handle write lock properly in mhi_pm_m0_transition

Take write lock only to protect db_mode member of mhi channel.
This allows rest of the mhi channels to just take read lock which
fine grains the locking. It prevents channel readers to starve if
they try to enter critical section after a writer.

Signed-off-by: Hemant Kumar <[email protected]>
---
drivers/bus/mhi/core/pm.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/bus/mhi/core/pm.c b/drivers/bus/mhi/core/pm.c
index 345f197..de5abb2 100644
--- a/drivers/bus/mhi/core/pm.c
+++ b/drivers/bus/mhi/core/pm.c
@@ -288,14 +288,18 @@ int mhi_pm_m0_transition(struct mhi_controller *mhi_cntrl)
for (i = 0; i < mhi_cntrl->max_chan; i++, mhi_chan++) {
struct mhi_ring *tre_ring = &mhi_chan->tre_ring;

- write_lock_irq(&mhi_chan->lock);
- if (mhi_chan->db_cfg.reset_req)
+ if (mhi_chan->db_cfg.reset_req) {
+ write_lock_irq(&mhi_chan->lock);
mhi_chan->db_cfg.db_mode = true;
+ write_unlock_irq(&mhi_chan->lock);
+ }
+
+ read_lock_irq(&mhi_chan->lock);

/* Only ring DB if ring is not empty */
if (tre_ring->base && tre_ring->wp != tre_ring->rp)
mhi_ring_chan_db(mhi_cntrl, mhi_chan);
- write_unlock_irq(&mhi_chan->lock);
+ read_unlock_irq(&mhi_chan->lock);
}

mhi_cntrl->wake_put(mhi_cntrl, false);
--
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project

2020-05-12 06:59:39

by Manivannan Sadhasivam

Subject: Re: [PATCH v1 5/5] bus: mhi: core: Handle write lock properly in mhi_pm_m0_transition

On Mon, May 11, 2020 at 07:03:09PM -0700, Hemant Kumar wrote:
> Take write lock only to protect db_mode member of mhi channel.
> This allows rest of the mhi channels to just take read lock which
> fine grains the locking. It prevents channel readers to starve if
> they try to enter critical section after a writer.
>
> Signed-off-by: Hemant Kumar <[email protected]>

Reviewed-by: Manivannan Sadhasivam <[email protected]>

Thanks,
Mani

> ---
> drivers/bus/mhi/core/pm.c | 10 +++++++---
> 1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/bus/mhi/core/pm.c b/drivers/bus/mhi/core/pm.c
> index 345f197..de5abb2 100644
> --- a/drivers/bus/mhi/core/pm.c
> +++ b/drivers/bus/mhi/core/pm.c
> @@ -288,14 +288,18 @@ int mhi_pm_m0_transition(struct mhi_controller *mhi_cntrl)
> for (i = 0; i < mhi_cntrl->max_chan; i++, mhi_chan++) {
> struct mhi_ring *tre_ring = &mhi_chan->tre_ring;
>
> - write_lock_irq(&mhi_chan->lock);
> - if (mhi_chan->db_cfg.reset_req)
> + if (mhi_chan->db_cfg.reset_req) {
> + write_lock_irq(&mhi_chan->lock);
> mhi_chan->db_cfg.db_mode = true;
> + write_unlock_irq(&mhi_chan->lock);
> + }
> +
> + read_lock_irq(&mhi_chan->lock);
>
> /* Only ring DB if ring is not empty */
> if (tre_ring->base && tre_ring->wp != tre_ring->rp)
> mhi_ring_chan_db(mhi_cntrl, mhi_chan);
> - write_unlock_irq(&mhi_chan->lock);
> + read_unlock_irq(&mhi_chan->lock);
> }
>
> mhi_cntrl->wake_put(mhi_cntrl, false);
> --
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> a Linux Foundation Collaborative Project