linux-kernel - Re: [PATCH v3] PCI: aardvark: Don't rely on jiffies while holding spinlock

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Message-ID: <20191015111623.GA7193@e121166-lin.cambridge.arm.com>
Date:   Tue, 15 Oct 2019 12:16:24 +0100
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     Remi Pommarel <repk@...plefau.lt>
Cc:     Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] PCI: aardvark: Don't rely on jiffies while holding
 spinlock

On Fri, Sep 27, 2019 at 10:55:02AM +0200, Remi Pommarel wrote:
> advk_pcie_wait_pio() can be called while holding a spinlock (from
> pci_bus_read_config_dword()), then depends on jiffies in order to
> timeout while polling on PIO state registers. In the case the PIO
> transaction failed, the timeout will never happen and will also cause
> the cpu to stall.
> 
> This decrements a variable and wait instead of using jiffies.
> 
> Signed-off-by: Remi Pommarel <repk@...plefau.lt>
> ---
> Changes since v1:
>   - Reduce polling delay
>   - Change size_t into int for loop counter
> Changes since v2:
>   - Keep timeout to 1ms by increasing retry counter
> ---
>  drivers/pci/controller/pci-aardvark.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)

Applied to pci/aardvark, thanks.

Lorenzo

> diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c
> index fc0fe4d4de49..7b5c9d6c8706 100644
> --- a/drivers/pci/controller/pci-aardvark.c
> +++ b/drivers/pci/controller/pci-aardvark.c
> @@ -175,7 +175,8 @@
>  	(PCIE_CONF_BUS(bus) | PCIE_CONF_DEV(PCI_SLOT(devfn))	| \
>  	 PCIE_CONF_FUNC(PCI_FUNC(devfn)) | PCIE_CONF_REG(where))
>  
> -#define PIO_TIMEOUT_MS			1
> +#define PIO_RETRY_CNT			500
> +#define PIO_RETRY_DELAY			2 /* 2 us*/
>  
>  #define LINK_WAIT_MAX_RETRIES		10
>  #define LINK_WAIT_USLEEP_MIN		90000
> @@ -383,17 +384,16 @@ static void advk_pcie_check_pio_status(struct advk_pcie *pcie)
>  static int advk_pcie_wait_pio(struct advk_pcie *pcie)
>  {
>  	struct device *dev = &pcie->pdev->dev;
> -	unsigned long timeout;
> +	int i;
>  
> -	timeout = jiffies + msecs_to_jiffies(PIO_TIMEOUT_MS);
> -
> -	while (time_before(jiffies, timeout)) {
> +	for (i = 0; i < PIO_RETRY_CNT; i++) {
>  		u32 start, isr;
>  
>  		start = advk_readl(pcie, PIO_START);
>  		isr = advk_readl(pcie, PIO_ISR);
>  		if (!start && isr)
>  			return 0;
> +		udelay(PIO_RETRY_DELAY);
>  	}
>  
>  	dev_err(dev, "config read/write timed out\n");
> -- 
> 2.20.1
>