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Message-ID: <f99d957b-7494-4f89-aa06-8016593301d2@quicinc.com>
Date: Wed, 6 Mar 2024 13:37:30 -0800
From: Unnathi Chalicheemala <quic_uchalich@...cinc.com>
To: Bjorn Andersson <quic_bjorande@...cinc.com>
CC: Bjorn Andersson <andersson@...nel.org>,
Konrad Dybcio
<konrad.dybcio@...aro.org>,
Sibi Sankar <quic_sibis@...cinc.com>, <linux-arm-msm@...r.kernel.org>,
<linux-kernel@...r.kernel.org>, <kernel@...cinc.com>,
Prasad Sodagudi <quic_psodagud@...cinc.com>,
"Murali
Nalajala" <quic_mnalajal@...cinc.com>,
Satya Durga Srinivasu Prabhala
<quic_satyap@...cinc.com>
Subject: Re: [PATCH 2/3] firmware: qcom-scm: Support multiple waitq contexts
On 3/5/2024 2:28 PM, Bjorn Andersson wrote:
> On Wed, Feb 28, 2024 at 10:50:00AM -0800, Unnathi Chalicheemala wrote:
>> Currently, only a single waitqueue context is supported, with waitqueue
>> id zero. SM8650 firmware now supports multiple waitqueue contexts, so
>> add support to dynamically create and support as many unique waitqueue
>> contexts as firmware returns to the driver.
>> Unique waitqueue contexts are supported using xarray to create a
>> hash table for associating a unique wq_ctx with a struct completion
>> variable for easy lookup.
>> The waitqueue ids can be >=0 as now we have more than one waitqueue
>> context.
>>
>> Signed-off-by: Unnathi Chalicheemala <quic_uchalich@...cinc.com>
>> ---
>> drivers/firmware/qcom/qcom_scm-smc.c | 7 +++-
>> drivers/firmware/qcom/qcom_scm.c | 77 ++++++++++++++++++++++++++----------
>> drivers/firmware/qcom/qcom_scm.h | 3 +-
>> 3 files changed, 64 insertions(+), 23 deletions(-)
>>
>> diff --git a/drivers/firmware/qcom/qcom_scm-smc.c b/drivers/firmware/qcom/qcom_scm-smc.c
>> index 16cf88acfa8e..80083e3615b1 100644
>> --- a/drivers/firmware/qcom/qcom_scm-smc.c
>> +++ b/drivers/firmware/qcom/qcom_scm-smc.c
>> @@ -103,7 +103,12 @@ static int __scm_smc_do_quirk_handle_waitq(struct device *dev, struct arm_smccc_
>> wq_ctx = res->a1;
>> smc_call_ctx = res->a2;
>>
>> - ret = qcom_scm_wait_for_wq_completion(wq_ctx);
>> + if (!dev) {
>> + /* Protect the dev_get_drvdata() call that follows */
>> + return -EPROBE_DEFER;
>
> No client driver will be prepared to handle an EPROBE_DEFER from here.
>
>> + }
>> +
>> + ret = qcom_scm_wait_for_wq_completion(dev_get_drvdata(dev), wq_ctx);
>
> I think it's fine to just continue to rely on __scm in the callee. If
> you don't agree, please consider this a separate cleanup patch.
>
Yes, sure. I will remove the !dev check.
>> if (ret)
>> return ret;
>>
>> diff --git a/drivers/firmware/qcom/qcom_scm.c b/drivers/firmware/qcom/qcom_scm.c
>> index c1be8270ead1..4606c49ef155 100644
>> --- a/drivers/firmware/qcom/qcom_scm.c
>> +++ b/drivers/firmware/qcom/qcom_scm.c
>>
>> -static int qcom_scm_assert_valid_wq_ctx(u32 wq_ctx)
>> +static struct completion *qcom_scm_get_completion(struct qcom_scm *scm, u32 wq_ctx)
>> {
>> - /* FW currently only supports a single wq_ctx (zero).
>> - * TODO: Update this logic to include dynamic allocation and lookup of
>> - * completion structs when FW supports more wq_ctx values.
>> + struct completion *wq;
>> + struct completion *old;
>> + int err;
>> +
>> + wq = xa_load(&scm->waitq, wq_ctx);
>
> What happens if qcom_scm_waitq_wakeup() is invoked concurrently with
> qcom_scm_waitq_wakeup(), such that both find wq = NULL here?
>
Ack. Thanks, I didn't check this race condition. I will define a mutex to check for
wq=NULL before creating one.
>> + if (wq) {
>> + /*
>> + * Valid struct completion *wq found corresponding to
>> + * given wq_ctx. We're done here.
>> + */
>> + goto out;
>> + }
>> +
>> + /*
>> + * If a struct completion *wq does not exist for wq_ctx, create it. FW
>> + * only uses a finite number of wq_ctx values, so we will be reaching
>> + * here only a few times right at the beginning of the device's uptime
>
> I'm confused, when I reviewed this previously I expressed that unless "a
> few" is more than 73, or that the value space is sparse, the use of an
> xarray only complicates the implementation.
>
> Either describe why this wouldn't work, or use a statically sized array.
>
Sorry I missed this comment. I'll check and change this to a static array
in the next version.
>> + * and then early-exit from idr_find() above subsequently.
>> */
>> - if (wq_ctx != 0) {
>> - dev_err(__scm->dev, "Firmware unexpectedly passed non-zero wq_ctx\n");
>> - return -EINVAL;
>> + wq = kzalloc(sizeof(*wq), GFP_ATOMIC);
>> + if (!wq) {
>> + wq = ERR_PTR(-ENOMEM);
>> + goto out;
>> }
>>
>> - return 0;
>> + init_completion(wq);
>> +
>> + old = xa_store(&scm->waitq, wq_ctx, wq, GFP_ATOMIC);
>> + err = xa_err(old);
>> + if (err) {
>> + kfree(wq);
>> + wq = ERR_PTR(err);
>> + }
>> +
>> +out:
>> + return wq;
>> }
>>
>> -int qcom_scm_wait_for_wq_completion(u32 wq_ctx)
>> +int qcom_scm_wait_for_wq_completion(struct qcom_scm *scm, u32 wq_ctx)
>> {
>> - int ret;
>> + struct completion *wq;
>>
>> - ret = qcom_scm_assert_valid_wq_ctx(wq_ctx);
>> - if (ret)
>> - return ret;
>> + wq = qcom_scm_get_completion(scm, wq_ctx);
>> + if (IS_ERR(wq)) {
>> + pr_err("Unable to wait on invalid waitqueue for wq_ctx %d: %ld\n",
>
> You don't attempt to wait until a few lines further down, so this error
> message doesn't seem to reflect the actual problem that occurred. Seems
> like this will only ever be ENOMEM in practice, in which case we
> shouldn't print an error, right?
>
> dev_err() seems suitable if this remains though.
>
Ack. You're right; will use dev_err().
>> + wq_ctx, PTR_ERR(wq));
>> + return PTR_ERR(wq);
>> + }
>>
>> - wait_for_completion(&__scm->waitq_comp);
>> + wait_for_completion(wq);
>>
>> return 0;
>> }
>>
>> static int qcom_scm_waitq_wakeup(struct qcom_scm *scm, unsigned int wq_ctx)
>> {
>> - int ret;
>> + struct completion *wq;
>>
>> - ret = qcom_scm_assert_valid_wq_ctx(wq_ctx);
>> - if (ret)
>> - return ret;
>> + wq = qcom_scm_get_completion(scm, wq_ctx);
>> + if (IS_ERR(wq)) {
>> + pr_err("Unable to wake up invalid waitqueue for wq_ctx %d: %ld\n",
>
> As above.
>
Ack. Thanks a lot for the review Bjorn!
> Regards,
> Bjorn
>
>> + wq_ctx, PTR_ERR(wq));
>> + return PTR_ERR(wq);
>> + }
>>
>> - complete(&__scm->waitq_comp);
>> + complete(wq);
>>
>> return 0;
>> }
>> @@ -1854,7 +1887,9 @@ static int qcom_scm_probe(struct platform_device *pdev)
>> if (ret)
>> return ret;
>>
>> - init_completion(&scm->waitq_comp);
>> + platform_set_drvdata(pdev, scm);
>> +
>> + xa_init(&scm->waitq);
>>
>> __scm = scm;
>> __scm->dev = &pdev->dev;
>> diff --git a/drivers/firmware/qcom/qcom_scm.h b/drivers/firmware/qcom/qcom_scm.h
>> index 4532907e8489..d54df5a2b690 100644
>> --- a/drivers/firmware/qcom/qcom_scm.h
>> +++ b/drivers/firmware/qcom/qcom_scm.h
>> @@ -62,7 +62,8 @@ struct qcom_scm_res {
>> u64 result[MAX_QCOM_SCM_RETS];
>> };
>>
>> -int qcom_scm_wait_for_wq_completion(u32 wq_ctx);
>> +struct qcom_scm;
>> +int qcom_scm_wait_for_wq_completion(struct qcom_scm *scm, u32 wq_ctx);
>> int scm_get_wq_ctx(u32 *wq_ctx, u32 *flags, u32 *more_pending);
>>
>> #define SCM_SMC_FNID(s, c) ((((s) & 0xFF) << 8) | ((c) & 0xFF))
>>
>> --
>> 2.25.1
>>
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