Re: [PATCH] PCI: aardvark: Implement re-issuing config requests on CRS response

[Pali Rohár]

On Monday 23 August 2021 14:02:14 Pali Rohár wrote:
> Commit 43f5c77bcbd2 ("PCI: aardvark: Fix reporting CRS value") fixed
> handling of CRS response and when CRSSVE flag was not enabled it marked CRS
> response as failed transaction (due to simplicity).
> 
> But pci-aardvark.c driver is already waiting up to the PIO_RETRY_CNT count
> for PIO config response and implementation of re-issuing config requests
> according to PCIe base specification is therefore simple.
> 
> This change implements re-issuing of config requests when response is CRS.
> And to prevent infinite loop set upper bound to around PIO_RETRY_CNT value,
> after which is transaction marked as failed and 0xFFFFFFFF is returned like
> before.
> 
> Implementation is done by returning appropriate error codes from function
> advk_pcie_check_pio_status(). On CRS is returned -EAGAIN and caller then
> reissue transaction up to the PIO_RETRY_CNT count. As advk_pcie_wait_pio()
> function waits some cycles, return number of these cycles and add them to
> the retry count. So the total time for config request would be only linear
> O(PIO_RETRY_CNT) and not quadratic O(PIO_RETRY_CNT^2) in the worst case.
> 
> Signed-off-by: Pali Rohár <pali@xxxxxxxxxx>
> Fixes: 43f5c77bcbd2 ("PCI: aardvark: Fix reporting CRS value")

Hello! Could you review this patch?

> ---
>  drivers/pci/controller/pci-aardvark.c | 36 ++++++++++++++++++++++-----
>  1 file changed, 30 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c
> index abc93225ba20..99f244190eae 100644
> --- a/drivers/pci/controller/pci-aardvark.c
> +++ b/drivers/pci/controller/pci-aardvark.c
> @@ -470,6 +470,7 @@ static int advk_pcie_check_pio_status(struct advk_pcie *pcie, bool allow_crs, u3
>  	u32 reg;
>  	unsigned int status;
>  	char *strcomp_status, *str_posted;
> +	int ret;
>  
>  	reg = advk_readl(pcie, PIO_STAT);
>  	status = (reg & PIO_COMPLETION_STATUS_MASK) >>
> @@ -494,6 +495,7 @@ static int advk_pcie_check_pio_status(struct advk_pcie *pcie, bool allow_crs, u3
>  	case PIO_COMPLETION_STATUS_OK:
>  		if (reg & PIO_ERR_STATUS) {
>  			strcomp_status = "COMP_ERR";
> +			ret = -EFAULT;
>  			break;
>  		}
>  		/* Get the read result */
> @@ -501,9 +503,11 @@ static int advk_pcie_check_pio_status(struct advk_pcie *pcie, bool allow_crs, u3
>  			*val = advk_readl(pcie, PIO_RD_DATA);
>  		/* No error */
>  		strcomp_status = NULL;
> +		ret = 0;
>  		break;
>  	case PIO_COMPLETION_STATUS_UR:
>  		strcomp_status = "UR";
> +		ret = -EOPNOTSUPP;
>  		break;
>  	case PIO_COMPLETION_STATUS_CRS:
>  		if (allow_crs && val) {
> @@ -521,6 +525,7 @@ static int advk_pcie_check_pio_status(struct advk_pcie *pcie, bool allow_crs, u3
>  			 */
>  			*val = CFG_RD_CRS_VAL;
>  			strcomp_status = NULL;
> +			ret = 0;
>  			break;
>  		}
>  		/* PCIe r4.0, sec 2.3.2, says:
> @@ -536,21 +541,24 @@ static int advk_pcie_check_pio_status(struct advk_pcie *pcie, bool allow_crs, u3
>  		 * Request and taking appropriate action, e.g., complete the
>  		 * Request to the host as a failed transaction.
>  		 *
> -		 * To simplify implementation do not re-issue the Configuration
> -		 * Request and complete the Request as a failed transaction.
> +		 * So return -EAGAIN and caller (pci-aardvark.c driver) will
> +		 * re-issue request again up to the PIO_RETRY_CNT retries.
>  		 */
>  		strcomp_status = "CRS";
> +		ret = -EAGAIN;
>  		break;
>  	case PIO_COMPLETION_STATUS_CA:
>  		strcomp_status = "CA";
> +		ret = -ECANCELED;
>  		break;
>  	default:
>  		strcomp_status = "Unknown";
> +		ret = -EINVAL;
>  		break;
>  	}
>  
>  	if (!strcomp_status)
> -		return 0;
> +		return ret;
>  
>  	if (reg & PIO_NON_POSTED_REQ)
>  		str_posted = "Non-posted";
> @@ -560,7 +568,7 @@ static int advk_pcie_check_pio_status(struct advk_pcie *pcie, bool allow_crs, u3
>  	dev_err(dev, "%s PIO Response Status: %s, %#x @ %#x\n",
>  		str_posted, strcomp_status, reg, advk_readl(pcie, PIO_ADDR_LS));
>  
> -	return -EFAULT;
> +	return ret;
>  }
>  
>  static int advk_pcie_wait_pio(struct advk_pcie *pcie)
> @@ -568,13 +576,13 @@ static int advk_pcie_wait_pio(struct advk_pcie *pcie)
>  	struct device *dev = &pcie->pdev->dev;
>  	int i;
>  
> -	for (i = 0; i < PIO_RETRY_CNT; i++) {
> +	for (i = 1; 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;
> +			return i;
>  		udelay(PIO_RETRY_DELAY);
>  	}
>  
> @@ -764,6 +772,7 @@ static int advk_pcie_rd_conf(struct pci_bus *bus, u32 devfn,
>  			     int where, int size, u32 *val)
>  {
>  	struct advk_pcie *pcie = bus->sysdata;
> +	int retry_count;
>  	bool allow_crs;
>  	u32 reg;
>  	int ret;
> @@ -816,6 +825,9 @@ static int advk_pcie_rd_conf(struct pci_bus *bus, u32 devfn,
>  	/* Program the data strobe */
>  	advk_writel(pcie, 0xf, PIO_WR_DATA_STRB);
>  
> +	retry_count = 0;
> +
> +retry:
>  	/* Clear PIO DONE ISR and start the transfer */
>  	advk_writel(pcie, 1, PIO_ISR);
>  	advk_writel(pcie, 1, PIO_START);
> @@ -834,8 +846,12 @@ static int advk_pcie_rd_conf(struct pci_bus *bus, u32 devfn,
>  		return PCIBIOS_SET_FAILED;
>  	}
>  
> +	retry_count += ret;
> +
>  	/* Check PIO status and get the read result */
>  	ret = advk_pcie_check_pio_status(pcie, allow_crs, val);
> +	if (ret == -EAGAIN && retry_count < PIO_RETRY_CNT)
> +		goto retry;
>  	if (ret < 0) {
>  		*val = 0xffffffff;
>  		return PCIBIOS_SET_FAILED;
> @@ -855,6 +871,7 @@ static int advk_pcie_wr_conf(struct pci_bus *bus, u32 devfn,
>  	struct advk_pcie *pcie = bus->sysdata;
>  	u32 reg;
>  	u32 data_strobe = 0x0;
> +	int retry_count;
>  	int offset;
>  	int ret;
>  
> @@ -896,6 +913,9 @@ static int advk_pcie_wr_conf(struct pci_bus *bus, u32 devfn,
>  	/* Program the data strobe */
>  	advk_writel(pcie, data_strobe, PIO_WR_DATA_STRB);
>  
> +	retry_count = 0;
> +
> +retry:
>  	/* Clear PIO DONE ISR and start the transfer */
>  	advk_writel(pcie, 1, PIO_ISR);
>  	advk_writel(pcie, 1, PIO_START);
> @@ -904,7 +924,11 @@ static int advk_pcie_wr_conf(struct pci_bus *bus, u32 devfn,
>  	if (ret < 0)
>  		return PCIBIOS_SET_FAILED;
>  
> +	retry_count += ret;
> +
>  	ret = advk_pcie_check_pio_status(pcie, false, NULL);
> +	if (ret == -EAGAIN && retry_count < PIO_RETRY_CNT)
> +		goto retry;
>  	if (ret < 0)
>  		return PCIBIOS_SET_FAILED;
>  
> -- 
> 2.20.1
>