linux-kernel - Re: Re: [PATCH] spi: spi-zynqmp-gqspi: Fix runtime PM imbalance in zynqmp_qspi

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Date:   Fri, 9 Apr 2021 15:53:37 +0800 (GMT+08:00)
From:   dinghao.liu@....edu.cn
To:     "quanyang.wang" <quanyang.wang@...driver.com>
Cc:     "Michal Simek" <michal.simek@...inx.com>, kjlu@....edu,
        "Amit Kumar Mahapatra" <amit.kumar-mahapatra@...inx.com>,
        "Mark Brown" <broonie@...nel.org>, linux-spi@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: Re: [PATCH] spi: spi-zynqmp-gqspi: Fix runtime PM imbalance in
 zynqmp_qspi_probe

> Hi Dinghao,
> 
> On 4/8/21 6:33 PM, Michal Simek wrote:
> > ++
> >
> > On 4/8/21 11:25 AM, Dinghao Liu wrote:
> >> When platform_get_irq() fails, a pairing PM usage counter
> >> increment is needed to keep the counter balanced. It's the
> >> same for the following error paths.
> >>
> >> Signed-off-by: Dinghao Liu <dinghao.liu@....edu.cn>
> >> ---
> >>   drivers/spi/spi-zynqmp-gqspi.c | 1 +
> >>   1 file changed, 1 insertion(+)
> >>
> >> diff --git a/drivers/spi/spi-zynqmp-gqspi.c b/drivers/spi/spi-zynqmp-gqspi.c
> >> index c8fa6ee18ae7..95963a2de64a 100644
> >> --- a/drivers/spi/spi-zynqmp-gqspi.c
> >> +++ b/drivers/spi/spi-zynqmp-gqspi.c
> >> @@ -1197,6 +1197,7 @@ static int zynqmp_qspi_probe(struct platform_device *pdev)
> >>   	return 0;
> >>   
> >>   clk_dis_all:
> >> +	pm_runtime_get_noresume(&pdev->dev);
> >>   	pm_runtime_set_suspended(&pdev->dev);
> >>   	pm_runtime_disable(&pdev->dev);
> >>   	clk_disable_unprepare(xqspi->refclk);
> >>
> The imbalance is because pm_runtime_put_autosuspend is called to make 
> counter to be -1.
> 
> It looks strange that there is no counter increament op before 
> pm_runtime_put_autosuspend.
> 
> In my limited understanding, it should look like:
> 
> ......
> 
> pm_runtime_enable
> 
> pm_runtime_get_sync   //increase counter to one to resume device
> 
> DO OPERATIONS HERE
> 
> pm_runtime_mark_last_busy
> pm_runtime_put_autosuspend   //decrease counter to zero and trigger suspend
> 
> return 0;
> 
> error_path:
> 
> pm_runtime_put_sync
> 
> pm_runtime_disable
> 
> return err;
> 
> 
> Am I missing something?
> 

Thanks for point out this! Usually there is an increment refcount in a 
_probe function and a decrement refcount in a _remove function. Sometimes 
the refcount decrement is in the _probe and the increment is in the _remove. 
But the refcount is balanced in both cases. So I think zynqmp_qspi_remove()
needs a refcount increment to fix this bug.

Regards,
Dinghao