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Date: Sat, 11 Sep 2021 01:13:55 +0200
From: Pali Rohár <pali@...nel.org>
To: Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
Bjorn Helgaas <bhelgaas@...gle.com>,
Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Cc: Marek Behún <kabel@...nel.org>,
Krzysztof Wilczyński <kw@...ux.com>,
linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI: aardvark: Implement re-issuing config requests on
CRS response
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@...nel.org>
> 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
>
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