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Date: Tue, 20 Jul 2021 16:49:55 +0200
From: Pali Rohár <pali@...nel.org>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
Bjorn Helgaas <bhelgaas@...gle.com>,
Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
Marek Behún <kabel@...nel.org>,
linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RESEND PATCH 2/3] PCI: aardvark: Fix checking for PIO status
On Monday 19 July 2021 18:12:27 Bjorn Helgaas wrote:
> On Fri, Jun 25, 2021 at 12:04:29PM +0100, Lorenzo Pieralisi wrote:
> > On Thu, Jun 24, 2021 at 11:33:44PM +0200, Pali Rohár wrote:
> >
> > [...]
> >
> > > -static void advk_pcie_check_pio_status(struct advk_pcie *pcie)
> > > +static int advk_pcie_check_pio_status(struct advk_pcie *pcie, u32 *val)
> > > {
> > > struct device *dev = &pcie->pdev->dev;
> > > u32 reg;
> > > @@ -472,15 +476,50 @@ static void advk_pcie_check_pio_status(struct advk_pcie *pcie)
> > > status = (reg & PIO_COMPLETION_STATUS_MASK) >>
> > > PIO_COMPLETION_STATUS_SHIFT;
> > >
> > > - if (!status)
> > > - return;
> > > -
> > > + /*
> > > + * According to HW spec, the PIO status check sequence as below:
> > > + * 1) even if COMPLETION_STATUS(bit9:7) indicates successful,
> > > + * it still needs to check Error Status(bit11), only when this bit
> > > + * indicates no error happen, the operation is successful.
> > > + * 2) value Unsupported Request(1) of COMPLETION_STATUS(bit9:7) only
> > > + * means a PIO write error, and for PIO read it is successful with
> > > + * a read value of 0xFFFFFFFF.
> > > + * 3) value Completion Retry Status(CRS) of COMPLETION_STATUS(bit9:7)
> > > + * only means a PIO write error, and for PIO read it is successful
> > > + * with a read value of 0xFFFF0001.
> > > + * 4) value Completer Abort (CA) of COMPLETION_STATUS(bit9:7) means
> > > + * error for both PIO read and PIO write operation.
> > > + * 5) other errors are indicated as 'unknown'.
> > > + */
> > > switch (status) {
> > > + case PIO_COMPLETION_STATUS_OK:
> > > + if (reg & PIO_ERR_STATUS) {
> > > + strcomp_status = "COMP_ERR";
> > > + break;
> > > + }
> > > + /* Get the read result */
> > > + if (val)
> > > + *val = advk_readl(pcie, PIO_RD_DATA);
> > > + /* No error */
> > > + strcomp_status = NULL;
> > > + break;
> > > case PIO_COMPLETION_STATUS_UR:
> > > - strcomp_status = "UR";
> > > + if (val) {
> > > + /* For reading, UR is not an error status */
> > > + *val = CFG_RD_UR_VAL;
>
> I think the comment is incorrect. Unsupported Request *is* an error
> status. But most platforms log it and fabricate ~0 data
> (CFG_RD_UR_VAL) to return to the CPU, and I think that's what you're
> doing here. So I think the code is fine, but the "not an error
> status" comment is wrong.
Ok, and what we should driver set as return value for pci_ops.read
callback in this case?
> Per the flowchart in PCIe r5.0, sec 6.2.5., fig 6-2, I think the
> hardware should be setting the "Unsupported Request Detected" bit in
> the Device Status register when this occurs.
Yes there is register in kernel's emulated PCIe bridge which at bit 19
has: Unsupported Request Detected - The core sets this bit to 1 when an
unsupported request is received. Write this bit to 1 to clear.
> > > + strcomp_status = NULL;
> > > + } else {
> > > + strcomp_status = "UR";
> > > + }
> > > break;
> > > case PIO_COMPLETION_STATUS_CRS:
> > > - strcomp_status = "CRS";
> > > + if (val) {
> > > + /* For reading, CRS is not an error status */
> > > + *val = CFG_RD_CRS_VAL;
> >
> > Need Bjorn's input on this. I don't think this is what is expected from
> > from a root complex according to the PCI specifications (depending on
> > whether CSR software visibility is supported or not).
> >
> > Here we are fabricating a CRS completion value for all PCI config read
> > transactions that are hitting a CRS completion status (and that's not
> > the expected behaviour according to the PCI specifications and I don't
> > think that's correct).
>
> Right. I think any config access (read or write) can be completed
> with a CRS completion (sec 2.3.1).
>
> Per sec 2.3.2, when CRS SV (in Root Control register, sec 7.5.3.12) is
> enabled and a config read that includes both bytes of the Vendor ID
> receives a CRS completion, we must return 0x0001 for the Vendor ID and
> 0xff for any additional bytes. Note that a config read of only the
> two Vendor ID bytes is legal and should receive 0x0001 data.
>
> But if CRS SV is disabled, I think config reads that receive CRS
> completions should fail the normal way, i.e., fabricate ~0 data.
In PCIe base 2.0 is:
For other Configuration Requests, or when CRS Software Visibility is not
enabled, the Root Complex will generally re-issue the Configuration
Request until it completes with a status other than CRS as described in
Section 2.3.2.
So what should pci-aardvark driver in this case do? Return ~0 or re-send
this config read request (and how many times)?
Also this relates to previous discussion about PCI_EXP_RTCTL_CRSSVE:
https://lore.kernel.org/linux-pci/20210507152542.sd54lk7bk56qapf3@pali/
> > > + strcomp_status = NULL;
> > > + } else {
> > > + strcomp_status = "CRS";
> > > + }
> > > break;
> > > case PIO_COMPLETION_STATUS_CA:
> > > strcomp_status = "CA";
> > > @@ -490,6 +529,9 @@ static void advk_pcie_check_pio_status(struct advk_pcie *pcie)
> > > break;
> > > }
> > >
> > > + if (!strcomp_status)
> > > + return 0;
> > > +
> > > if (reg & PIO_NON_POSTED_REQ)
> > > str_posted = "Non-posted";
> > > else
> > > @@ -497,6 +539,8 @@ static void advk_pcie_check_pio_status(struct advk_pcie *pcie)
> > >
> > > dev_err(dev, "%s PIO Response Status: %s, %#x @ %#x\n",
> > > str_posted, strcomp_status, reg, advk_readl(pcie, PIO_ADDR_LS));
> > > +
> > > + return -EFAULT;
> > > }
> > >
> > > static int advk_pcie_wait_pio(struct advk_pcie *pcie)
> > > @@ -703,8 +747,17 @@ static int advk_pcie_rd_conf(struct pci_bus *bus, u32 devfn,
> > > size, val);
> > >
> > > if (advk_pcie_pio_is_running(pcie)) {
> > > - *val = 0xffffffff;
> > > - return PCIBIOS_SET_FAILED;
> > > + /*
> > > + * For PCI_VENDOR_ID register, return Completion Retry Status
> > > + * so caller tries to issue the request again insted of failing
> > > + */
> > > + if (where == PCI_VENDOR_ID) {
> > > + *val = CFG_RD_CRS_VAL;
> > > + return PCIBIOS_SUCCESSFUL;
> >
> > Mmmm..here we are faking a CRS completion value to coerce the kernel
> > into believing a CRS completion was received (which is not necessarily
> > true) ?
> >
> > if advk_pcie_pio_is_running(pcie) == true, is that an HW error ?
> >
> > Lorenzo
> >
> > > + } else {
> > > + *val = 0xffffffff;
> > > + return PCIBIOS_SET_FAILED;
> > > + }
> > > }
> > >
> > > /* Program the control register */
> > > @@ -729,15 +782,27 @@ static int advk_pcie_rd_conf(struct pci_bus *bus, u32 devfn,
> > > advk_writel(pcie, 1, PIO_START);
> > >
> > > ret = advk_pcie_wait_pio(pcie);
> > > + if (ret < 0) {
> > > + /*
> > > + * For PCI_VENDOR_ID register, return Completion Retry Status
> > > + * so caller tries to issue the request again instead of failing
> > > + */
> > > + if (where == PCI_VENDOR_ID) {
> > > + *val = CFG_RD_CRS_VAL;
> > > + return PCIBIOS_SUCCESSFUL;
> > > + } else {
> > > + *val = 0xffffffff;
> > > + return PCIBIOS_SET_FAILED;
> > > + }
> > > + }
> > > +
> > > + /* Check PIO status and get the read result */
> > > + ret = advk_pcie_check_pio_status(pcie, val);
> > > if (ret < 0) {
> > > *val = 0xffffffff;
> > > return PCIBIOS_SET_FAILED;
> > > }
> > >
> > > - advk_pcie_check_pio_status(pcie);
> > > -
> > > - /* Get the read result */
> > > - *val = advk_readl(pcie, PIO_RD_DATA);
> > > if (size == 1)
> > > *val = (*val >> (8 * (where & 3))) & 0xff;
> > > else if (size == 2)
> > > @@ -801,7 +866,9 @@ static int advk_pcie_wr_conf(struct pci_bus *bus, u32 devfn,
> > > if (ret < 0)
> > > return PCIBIOS_SET_FAILED;
> > >
> > > - advk_pcie_check_pio_status(pcie);
> > > + ret = advk_pcie_check_pio_status(pcie, NULL);
> > > + if (ret < 0)
> > > + return PCIBIOS_SET_FAILED;
> > >
> > > return PCIBIOS_SUCCESSFUL;
> > > }
> > > --
> > > 2.20.1
> > >
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