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SubjectRe: [PATCH 1/2] PCI: mobiveil: ls_pcie_g4: add Workaround for A-011577
On Sun, Dec 02, 2018 at 01:32:42PM +0000, Z.q. Hou wrote:
> From: Hou Zhiqiang <Zhiqiang.Hou@nxp.com>

Can we pick one driver name (either "mobiveil" or "ls_pcie_g4" (this
seems excessively long and excessively specific), or something else)?
I don't want to waste the space of "PCI: mobiveil: ls_pcie_g4:" in
every future subject line.

Then "Add workaround for ...". I assume the "A-011577" part is
meaningful inside NXP, but it's not useful to anybody else. Move that
to the changelog proper and say something about the actual issue in
the subject.

> PCIe configuration access to non-existent function triggered
> SERROR interrupt exception.
>
> Workaround:
> Disable error reporting on AXI bus during the Vendor ID read
> transactions in enumeration.
>
> This ERRATA is only for LX2160A Rev1.0, and it will be fixed
> in Rev2.0.
>
> Signed-off-by: Hou Zhiqiang <Zhiqiang.Hou@nxp.com>
> ---
> .../controller/mobiveil/pci-layerscape-gen4.c | 24 +++++++++++++++++++
> .../controller/mobiveil/pcie-mobiveil-host.c | 13 +++++++++-
> .../pci/controller/mobiveil/pcie-mobiveil.h | 2 ++
> 3 files changed, 38 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/pci/controller/mobiveil/pci-layerscape-gen4.c b/drivers/pci/controller/mobiveil/pci-layerscape-gen4.c
> index 174cbcac4059..1fe56532b288 100644
> --- a/drivers/pci/controller/mobiveil/pci-layerscape-gen4.c
> +++ b/drivers/pci/controller/mobiveil/pci-layerscape-gen4.c
> @@ -24,6 +24,9 @@
>
> /* LUT and PF control registers */
> #define PCIE_LUT_OFF (0x80000)
> +#define PCIE_LUT_GCR (0x28)
> +#define PCIE_LUT_GCR_RRE (0)
> +
> #define PCIE_PF_OFF (0xc0000)
> #define PCIE_PF_INT_STAT (0x18)
> #define PF_INT_STAT_PABRST (31)
> @@ -188,8 +191,29 @@ static void ls_pcie_g4_reset(struct work_struct *work)
> ls_pcie_g4_reinit_hw(pcie);
> }
>
> +static int ls_pcie_g4_read_other_conf(struct pci_bus *bus, unsigned int devfn,
> + int where, int size, u32 *val)
> +{
> + struct mobiveil_pcie *pci = bus->sysdata;
> + struct ls_pcie_g4 *pcie = to_ls_pcie_g4(pci);
> + int ret;
> +
> + if (where == PCI_VENDOR_ID)
> + ls_pcie_g4_lut_writel(pcie, PCIE_LUT_GCR,
> + 0 << PCIE_LUT_GCR_RRE);
> +
> + ret = pci_generic_config_read(bus, devfn, where, size, val);
> +
> + if (where == PCI_VENDOR_ID)
> + ls_pcie_g4_lut_writel(pcie, PCIE_LUT_GCR,
> + 1 << PCIE_LUT_GCR_RRE);

1) As a general style rule, it's better to "clear, then restore" than
to "clear, then set" the bit. That way if somebody elsewhere decides
that PCIE_LUT_GCR_RRE should be cleared by default, this code won't
stomp on that decision. E.g.,

gcr = ls_pcie_g4_lut_readl(...);
ls_pcie_g4_lut_writel(..., 0 << PCIE_LUT_GCR_RRE);
ret = pci_generic_config_read(...);
ls_pcie_g4_lut_writel(..., gcr);

2) I don't *think* the PCIe spec requires that the first access to a
device be a read of the Vendor ID, so this is a 99% solution, not a
100% solution. A 100% solution would be to handle the SERROR so it's
not fatal. But I'm pretty sure Linux always does read the Vendor ID
first (except after a reset, and when we do config reads after a
reset, we already know the device *exists*), so this is probably
pretty safe.

> + return ret;
> +}
> +
> static struct mobiveil_rp_ops ls_pcie_g4_rp_ops = {
> .interrupt_init = ls_pcie_g4_interrupt_init,
> + .read_other_conf = ls_pcie_g4_read_other_conf,
> };
> static const struct mobiveil_pab_ops ls_pcie_g4_pab_ops = {
> diff --git a/drivers/pci/controller/mobiveil/pcie-mobiveil-host.c b/drivers/pci/controller/mobiveil/pcie-mobiveil-host.c
> index c85f00d3cfcf..8b6db38320d7 100644
> --- a/drivers/pci/controller/mobiveil/pcie-mobiveil-host.c
> +++ b/drivers/pci/controller/mobiveil/pcie-mobiveil-host.c
> @@ -79,9 +79,20 @@ static void __iomem *mobiveil_pcie_map_bus(struct pci_bus *bus,
> return pcie->rp.config_axi_slave_base + where;
> }
>
> +static int mobiveil_pcie_config_read(struct pci_bus *bus, unsigned int devfn,
> + int where, int size, u32 *val)
> +{
> + struct mobiveil_pcie *pcie = bus->sysdata;
> + struct root_port *rp = &pcie->rp;
> +
> + if (bus->number > rp->root_bus_nr && rp->ops->read_other_conf)
> + return rp->ops->read_other_conf(bus, devfn, where, size, val);
> +
> + return pci_generic_config_read(bus, devfn, where, size, val);
> +}
> static struct pci_ops mobiveil_pcie_ops = {
> .map_bus = mobiveil_pcie_map_bus,
> - .read = pci_generic_config_read,
> + .read = mobiveil_pcie_config_read,
> .write = pci_generic_config_write,
> };
>
> diff --git a/drivers/pci/controller/mobiveil/pcie-mobiveil.h b/drivers/pci/controller/mobiveil/pcie-mobiveil.h
> index 0ccd6cee5f8f..ef93b41f4419 100644
> --- a/drivers/pci/controller/mobiveil/pcie-mobiveil.h
> +++ b/drivers/pci/controller/mobiveil/pcie-mobiveil.h
> @@ -145,6 +145,8 @@ struct mobiveil_msi { /* MSI information */
>
> struct mobiveil_rp_ops {
> int (*interrupt_init)(struct mobiveil_pcie *pcie);
> + int (*read_other_conf)(struct pci_bus *bus, unsigned int devfn,
> + int where, int size, u32 *val);
> };
>
> struct root_port {
> --
> 2.17.1
>

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