linux-kernel - Re: [PATCH v9 2/3] firmware: qcom_scm: Support multiple waitq contexts

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Message-ID: <CAMRc=Mduqp1MaGZ2_Kfmb31WMntAW1FtAUgr1GBhGEy7PY21fg@mail.gmail.com>
Date: Tue, 25 Nov 2025 06:19:30 -0800
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Shivendra Pratap <shivendra.pratap@....qualcomm.com>
Cc: linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Unnathi Chalicheemala <unnathi.chalicheemala@....qualcomm.com>, 
	Bjorn Andersson <andersson@...nel.org>, Konrad Dybcio <konradybcio@...nel.org>
Subject: Re: [PATCH v9 2/3] firmware: qcom_scm: Support multiple waitq contexts

On Sun, 23 Nov 2025 15:19:31 +0100, Shivendra Pratap
<shivendra.pratap@....qualcomm.com> said:
> From: Unnathi Chalicheemala <unnathi.chalicheemala@....qualcomm.com>
>
> Currently, only a single waitqueue context exists in the driver.
> Multi-waitqueue mechanism is added in firmware to support the case,
> when multiple VMs make SMC calls or single VM making multiple calls on
> same CPU. Enhance the driver to support multiple waitqueue when
> support is present in the firmware.
>
> When VMs make a SMC call, firmware allocates a waitqueue context,
> assuming the SMC call to be a blocking call. The SMC calls that cannot
> acquire resources, while execution in firmware, are returned to sleep
> in the calling VM. When the resource becomes available in the
> firmware, the VM gets notified to wake the sleeping thread and resume
> SMC call. The current qcom_scm driver supports single waitqueue as the
> old firmwares support only single waitqueue with waitqueue id zero.
> Multi-waitqueue mechanism is added in firmware starting SM8650 to
> support the case when multiple VMs make SMC calls or single VM making
> multiple calls on same CPU. To enable this support in qcom_scm driver,
> add support for handling multiple waitqueues. For instance, SM8650
> firmware can allocate two such waitq contexts, so the driver needs to
> implement two waitqueue contexts. For a generalized approach, the
> number of supported waitqueues can be queried from the firmware using
> a SMC call.
>
> Introduce qcom_scm_query_waitq_count to get the number of waitqueue
> contexts supported by the firmware and allocate “N” unique waitqueue
> contexts with a dynamic sized array where each unique wq_ctx is
> associated with a struct completion variable for easy lookup. Older
> targets which support only a single waitqueue, may return an error for
> qcom_scm_query_waitq_count, set the wq_cnt to one for such failures.
>
> Signed-off-by: Unnathi Chalicheemala <unnathi.chalicheemala@....qualcomm.com>
> Signed-off-by: Shivendra Pratap <shivendra.pratap@....qualcomm.com>
> ---

Reviewed-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>