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Message-ID: <32baf45d-b118-4476-a30b-3ad461ffdf1d@quicinc.com>
Date: Wed, 6 Mar 2024 10:14:19 -0800
From: Unnathi Chalicheemala <quic_uchalich@...cinc.com>
To: Chris Lew <quic_clew@...cinc.com>, Bjorn Andersson <andersson@...nel.org>,
Konrad Dybcio <konrad.dybcio@...aro.org>,
Sibi Sankar
<quic_sibis@...cinc.com>
CC: <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 2/28/2024 3:20 PM, Chris Lew wrote:
>
>
> On 2/28/2024 10:50 AM, 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;
>> + }
>> +
>
> Do we need to do this !dev check within the do/while loop? Seems like it
> could be done once at the start.
>
Apologies for the late reply Chris.
Yes, will move this check out side the do {} while() loop.
>> + ret = qcom_scm_wait_for_wq_completion(dev_get_drvdata(dev), wq_ctx);
>> 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
>> @@ -21,6 +21,7 @@
>> #include <linux/platform_device.h>
>> #include <linux/reset-controller.h>
>> #include <linux/types.h>
>> +#include <linux/xarray.h>
>>
>> #include "qcom_scm.h"
>>
>> @@ -33,7 +34,7 @@ struct qcom_scm {
>> struct clk *iface_clk;
>> struct clk *bus_clk;
>> struct icc_path *path;
>> - struct completion waitq_comp;
>> + struct xarray waitq;
>> struct reset_controller_dev reset;
>>
>> /* control access to the interconnect path */
>> @@ -1742,42 +1743,74 @@ bool qcom_scm_is_available(void)
>> }
>> EXPORT_SYMBOL_GPL(qcom_scm_is_available);
>>
>> -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);
>> + 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
>> + * 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);
>> + }
>> +
>
> Any chance for this function to be called concurrently before there is a
> valid wq stored in the xarray? If that were to happen we could have two
> valid xa_stores happen on the same wq_ctx. One of the entries would be
> returned as old and might be leaked depending on timing.
>
Thanks for pointing this out. Yes, this function is called every time a
qcom_smc_call() is made. But xarray documentation says that xa_store() uses
an internal xa_lock to synchronize accesses - I will look more into this.
To prevent rewriting entries at same wq_ctx, I think xa_store can be replaced
with xa_insert() - it'll prevent rewrite on existing entry.
>> +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",
>> + 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",
>> + 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);
>
> Is there a benefit to having qcom_scm passed in? I see we're adding scm
> as drvdata in this patch, but we still have a single global __scm
> pointer in qcom_scm.c. Are there going to be multiple instances of the
> qcom_scm device?
>
I'll check and remove if possible.
Thanks a lot for the review Chris!
> Thanks,
> Chris
>
>> int scm_get_wq_ctx(u32 *wq_ctx, u32 *flags, u32 *more_pending);
>>
>> #define SCM_SMC_FNID(s, c) ((((s) & 0xFF) << 8) | ((c) & 0xFF))
>>
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