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Date:   Fri, 27 Apr 2018 10:55:36 -0600
From:   Lina Iyer <ilina@...eaurora.org>
To:     Matthias Kaehlcke <mka@...omium.org>
Cc:     andy.gross@...aro.org, david.brown@...aro.org,
        linux-arm-msm@...r.kernel.org, linux-soc@...r.kernel.org,
        rnayak@...eaurora.org, bjorn.andersson@...aro.org,
        linux-kernel@...r.kernel.org, sboyd@...nel.org,
        evgreen@...omium.org, dianders@...omium.org
Subject: Re: [PATCH v6 04/10] drivers: qcom: rpmh: add RPMH helper functions

On Thu, Apr 26 2018 at 12:05 -0600, Matthias Kaehlcke wrote:
>Hi Lina,
>
>On Thu, Apr 19, 2018 at 04:16:29PM -0600, Lina Iyer wrote:
>> Sending RPMH requests and waiting for response from the controller
>> through a callback is common functionality across all platform drivers.
>> To simplify drivers, add a library functions to create RPMH client and
>> send resource state requests.
>>
>> rpmh_write() is a synchronous blocking call that can be used to send
>> active state requests.
>>
>> Signed-off-by: Lina Iyer <ilina@...eaurora.org>
>> ---
>>
>> Changes in v6:
>> 	- replace rpmh_client with device
>> 	- inline wait_for_tx_done()
>>
>> Changes in v4:
>> 	- use const struct tcs_cmd in API
>> 	- remove wait count from this patch
>> 	- changed -EFAULT to -EINVAL
>> ---
>>  drivers/soc/qcom/Makefile        |   4 +-
>>  drivers/soc/qcom/rpmh-internal.h |   6 ++
>>  drivers/soc/qcom/rpmh-rsc.c      |   8 ++
>>  drivers/soc/qcom/rpmh.c          | 168 +++++++++++++++++++++++++++++++
>>  include/soc/qcom/rpmh.h          |  25 +++++
>>  5 files changed, 210 insertions(+), 1 deletion(-)
>>  create mode 100644 drivers/soc/qcom/rpmh.c
>>  create mode 100644 include/soc/qcom/rpmh.h
>>
>> diff --git a/drivers/soc/qcom/Makefile b/drivers/soc/qcom/Makefile
>> index cb6300f6a8e9..bb395c3202ca 100644
>> --- a/drivers/soc/qcom/Makefile
>> +++ b/drivers/soc/qcom/Makefile
>> @@ -7,7 +7,9 @@ obj-$(CONFIG_QCOM_PM)	+=	spm.o
>>  obj-$(CONFIG_QCOM_QMI_HELPERS)	+= qmi_helpers.o
>>  qmi_helpers-y	+= qmi_encdec.o qmi_interface.o
>>  obj-$(CONFIG_QCOM_RMTFS_MEM)	+= rmtfs_mem.o
>> -obj-$(CONFIG_QCOM_RPMH)	+=	rpmh-rsc.o
>> +obj-$(CONFIG_QCOM_RPMH)		+= qcom_rpmh.o
>> +qcom_rpmh-y			+= rpmh-rsc.o
>> +qcom_rpmh-y			+= rpmh.o
>>  obj-$(CONFIG_QCOM_SMD_RPM)	+= smd-rpm.o
>>  obj-$(CONFIG_QCOM_SMEM) +=	smem.o
>>  obj-$(CONFIG_QCOM_SMEM_STATE) += smem_state.o
>> diff --git a/drivers/soc/qcom/rpmh-internal.h b/drivers/soc/qcom/rpmh-internal.h
>> index cc29176f1303..d9a21726e568 100644
>> --- a/drivers/soc/qcom/rpmh-internal.h
>> +++ b/drivers/soc/qcom/rpmh-internal.h
>> @@ -14,6 +14,7 @@
>>  #define MAX_CMDS_PER_TCS		16
>>  #define MAX_TCS_PER_TYPE		3
>>  #define MAX_TCS_NR			(MAX_TCS_PER_TYPE * TCS_TYPE_NR)
>> +#define RPMH_MAX_CTRLR			2
>>
>>  struct rsc_drv;
>>
>> @@ -52,6 +53,7 @@ struct tcs_group {
>>   * @tcs:        TCS groups
>>   * @tcs_in_use: s/w state of the TCS
>>   * @lock:       synchronize state of the controller
>> + * @list:       element in list of drv
>>   */
>>  struct rsc_drv {
>>  	const char *name;
>> @@ -61,9 +63,13 @@ struct rsc_drv {
>>  	struct tcs_group tcs[TCS_TYPE_NR];
>>  	DECLARE_BITMAP(tcs_in_use, MAX_TCS_NR);
>>  	spinlock_t lock;
>> +	struct list_head list;
>>  };
>>
>> +extern struct list_head rsc_drv_list;
>>
>>  int rpmh_rsc_send_data(struct rsc_drv *drv, const struct tcs_request *msg);
>>
>> +void rpmh_tx_done(const struct tcs_request *msg, int r);
>                                                        ~
>
>nit: consider using a more expressive name, like status, rc, res or
>err.
>
OK. Will fix.

><snip>
>
>> +static struct rpmh_ctrlr *get_rpmh_ctrlr(const struct device *dev)
>> +{
>> +	int i;
>> +	struct rsc_drv *p, *drv = dev_get_drvdata(dev->parent);
>> +	struct rpmh_ctrlr *ctrlr = ERR_PTR(-EINVAL);
>> +
>> +	if (!drv)
>> +		return ctrlr;
>> +
>> +	for (i = 0; i < RPMH_MAX_CTRLR; i++) {
>> +		if (rpmh_rsc[i].drv == drv) {
>> +			ctrlr = &rpmh_rsc[i];
>> +			return ctrlr;
>> +		}
>> +	}
>> +
>> +	list_for_each_entry(p, &rsc_drv_list, list) {
>> +		if (drv == p) {
>> +			for (i = 0; i < RPMH_MAX_CTRLR; i++) {
>> +				if (!rpmh_rsc[i].drv)
>> +					break;
>> +			}
>> +			rpmh_rsc[i].drv = drv;
>
>There is a race condition, get_rpmh_ctrlr() could be executed
>simulatenously in different contexts, and select the same
>controller instance for different DRVs.
>
True. This will need to be serialized.

>It's probably an unlikely case, but to be safe you'd have to do
>something like this:
>
>retry:
>for (i = 0; i < RPMH_MAX_CTRLR; i++) {
>	if (!rpmh_rsc[i].drv)
>		break;
>}
>
>spin_lock(&rpmh_rsc[i].lock);
>
>if (!rpmh_rsc[i].drv) {
>	rpmh_rsc[i].drv = drv;
>	ctrlr = &rpmh_rsc[i];
>} else {
>	spin_unlock(&rpmh_rsc[i].lock);
>	goto retry;
>}
>
>spin_unlock(&rpmh_rsc[i].lock);
>
>
>The above code doesn't address another potential error case, where
>#DRV > RPMH_MAX_CTRLR. In this case we'd access memory beyond
>rpmh_rsc. This would be a configuration error, not sure if it's
>strictly necessary to handle it.
>
I think I might be able to solve for this a bit simpler with another
spinlock for the rpmh_rsc.

><snip>
>
>> +/**
>> + * rpmh_write: Write a set of RPMH commands and block until response
>> + *
>> + * @rc: The RPMh handle got from rpmh_get_client
>               ~~~~
>
>nit: Other than this the driver consistently uses 'RPMH'
>
OK.

Thanks for the review Matthias.

-- Lina

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