linux-kernel - Re: [PATCH v12 7/9] firmware: qcom: scm: Fix _

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Message-ID: <03367100-1ad4-4d83-8200-5879550398be@quicinc.com>
Date: Tue, 19 Mar 2024 06:47:40 +0530
From: Pavan Kondeti <quic_pkondeti@...cinc.com>
To: Mukesh Ojha <quic_mojha@...cinc.com>
CC: Bjorn Andersson <andersson@...nel.org>, <konrad.dybcio@...aro.org>,
        <linux-arm-msm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linus.walleij@...aro.org>, <linux-gpio@...r.kernel.org>
Subject: Re: [PATCH v12 7/9] firmware: qcom: scm: Fix __scm->dev assignement

On Mon, Mar 18, 2024 at 06:38:20PM +0530, Mukesh Ojha wrote:
> 
> 
> On 3/3/2024 12:55 AM, Bjorn Andersson wrote:
> > On Tue, Feb 27, 2024 at 09:23:06PM +0530, Mukesh Ojha wrote:
> > > qcom_scm_is_available() gives wrong indication if __scm
> > > is initialized but __scm->dev is not.
> > > 
> > > Fix this appropriately by making sure if __scm is
> > > initialized and then it is associated with its
> > > device.
> > > 
> > 
> > This seems like a bug fix, and should as such have a Fixes: tag and
> > probably Cc: stable@...r.kernel.org
> > 
> > > Signed-off-by: Mukesh Ojha <quic_mojha@...cinc.com>
> > > ---
> > >   drivers/firmware/qcom/qcom_scm.c | 2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/firmware/qcom/qcom_scm.c b/drivers/firmware/qcom/qcom_scm.c
> > > index 6c252cddd44e..6f14254c0c10 100644
> > > --- a/drivers/firmware/qcom/qcom_scm.c
> > > +++ b/drivers/firmware/qcom/qcom_scm.c
> > > @@ -1859,6 +1859,7 @@ static int qcom_scm_probe(struct platform_device *pdev)
> > >   	if (!scm)
> > >   		return -ENOMEM;
> > > +	scm->dev = &pdev->dev;
> > >   	ret = qcom_scm_find_dload_address(&pdev->dev, &scm->dload_mode_addr);
> > >   	if (ret < 0)
> > >   		return ret;
> > > @@ -1895,7 +1896,6 @@ static int qcom_scm_probe(struct platform_device *pdev)
> > >   		return ret;
> > >   	__scm = scm;
> > > -	__scm->dev = &pdev->dev;
> > 
> > Is it sufficient to just move the line up, or do we need a barrier of
> > some sort here?
> 
> Would be good to use, smp_mb() before the assignment
>      __scm = scm
> along with moving below line
> __scm->dev = &pdev->dev
> 

Full memory barrier is not needed here. store variant is sufficient.
WRITE_ONCE() + smp_store_release() will fit here no?

Thanks,
Pavan