Re: [PATCH 1/2] drivers: qcom: rpmh-rsc: simplify TCS locking

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On Fri, Jul 19 2019 at 12:20 -0600, Stephen Boyd wrote:
Quoting Lina Iyer (2019-07-01 08:29:06)
From: "Raju P.L.S.S.S.N" <rplsssn@xxxxxxxxxxxxxx>

tcs->lock was introduced to serialize access with in TCS group. But
even without tcs->lock, drv->lock is serving the same purpose. So
use a single drv->lock.

Isn't the downside now that we're going to be serializing access to the
different TCSes when two are being written in parallel or waited on? I
thought that was the whole point of splitting the lock into a TCS lock
and a general "driver" lock that protects the global driver state vs.
the specific TCS state.

Yes but we were holding the drv->lock as well as tcs->lock for the most
critical of the path anyways (writing to TCS). The added complexity
doesn't seem to help reduce the latency that it expected to reduce.

Other optimizations include -
 - Remove locking around clear_bit() in IRQ handler. clear_bit() is
 - Remove redundant read of TCS registers.
 - Use spin_lock instead of _irq variants as the locks are not held
   in interrupt context.

Can you please split this patch up into 3 or 4 different patches? I'm
not sure why any of these patches are marked with Fixes either. It's an
optimization patch, not a fix patch, unless the optimization is really
large somehow?

Okay. I will try that.

Fixes: 658628 ("drivers: qcom: rpmh-rsc: add RPMH controller for QCOM
Signed-off-by: Raju P.L.S.S.S.N <rplsssn@xxxxxxxxxxxxxx>
Signed-off-by: Lina Iyer <ilina@xxxxxxxxxxxxxx>
 drivers/soc/qcom/rpmh-internal.h |  2 --
 drivers/soc/qcom/rpmh-rsc.c      | 37 +++++++++++---------------------
 drivers/soc/qcom/rpmh.c          | 20 +++++++----------
 3 files changed, 21 insertions(+), 38 deletions(-)

diff --git a/drivers/soc/qcom/rpmh-internal.h b/drivers/soc/qcom/rpmh-internal.h
index a7bbbb67991c..969d5030860e 100644
--- a/drivers/soc/qcom/rpmh-internal.h
+++ b/drivers/soc/qcom/rpmh-internal.h
diff --git a/drivers/soc/qcom/rpmh-rsc.c b/drivers/soc/qcom/rpmh-rsc.c
index e278fc11fe5c..92461311aef3 100644
--- a/drivers/soc/qcom/rpmh-rsc.c
+++ b/drivers/soc/qcom/rpmh-rsc.c
@@ -93,8 +93,7 @@ static void write_tcs_reg_sync(struct rsc_drv *drv, int reg, int tcs_id,

 static bool tcs_is_free(struct rsc_drv *drv, int tcs_id)
-       return !test_bit(tcs_id, drv->tcs_in_use) &&
-              read_tcs_reg(drv, RSC_DRV_STATUS, tcs_id, 0);
+       return !test_bit(tcs_id, drv->tcs_in_use);

This can be a diffedjusted rent patch. Why is reading the tcs register
redundant? Please put that information in the commit text.

The tcs_in_use, is adjusted along with the DRV_STS and reading the
tcs_in_use should be enough.

Thanks for your review Stephen.


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