Re: [PATCH 3/5] PCI: st: Provide support for the sti PCIe controller

[Bjorn Helgaas]

On Wed, Dec 17, 2014 at 11:34:44AM +0100, Gabriel FERNANDEZ wrote:
> sti pcie is built around a Synopsis Designware PCIe IP.
> 
> Signed-off-by: Fabrice Gasnier <fabrice.gasnier@xxxxxx>
> Signed-off-by: Gabriel Fernandez <gabriel.fernandez@xxxxxxxxxx>
> ---
>  drivers/pci/host/Kconfig  |   5 +
>  drivers/pci/host/Makefile |   1 +
>  drivers/pci/host/pci-st.c | 713 ++++++++++++++++++++++++++++++++++++++++++++++

Hi Gabriel,

Can you add a MAINTAINERS update so I know who should ack changes to this
driver?

>  3 files changed, 719 insertions(+)
>  create mode 100644 drivers/pci/host/pci-st.c
> 
> diff --git a/drivers/pci/host/Kconfig b/drivers/pci/host/Kconfig
> index c4b6568..999d2b9 100644
> --- a/drivers/pci/host/Kconfig
> +++ b/drivers/pci/host/Kconfig
> @@ -102,4 +102,9 @@ config PCI_LAYERSCAPE
>  	help
>  	  Say Y here if you want PCIe controller support on Layerscape SoCs.
>  
> +config PCI_ST
> +	bool "ST STiH41x PCIe controller"
> +	depends on ARCH_STI
> +	select PCIE_DW

Please add help text here.

> +static int st_pcie_rd_other_conf(struct pcie_port *pp, struct pci_bus *bus,
> +				 unsigned int devfn, int where, int size,
> +				 u32 *val)
> +{
> +	u32 data;
> +	u32 bdf;
> +	struct st_pcie *pcie = to_st_pcie(pp);
> +	int is_root_bus = pci_is_root_bus(bus);
> +	int retry_count = 0;
> +	int ret;
> +	void __iomem *addr;
> +
> +	/*
> +	 * Prerequisite
> +	 * PCI express devices will respond to all config type 0 cycles, since
> +	 * they are point to point links. Thus to avoid probing for multiple
> +	 * devices on the root, dw-pcie already check for us if it is on the
> +	 * root bus / other slots. Also, dw-pcie checks for the link being up
> +	 * as we will hang if we issue a config request and the link is down.
> +	 * A switch will reject requests for slots it knows do not exist.
> +	 */
> +	bdf = bdf_num(bus->number, devfn, is_root_bus);
> +	addr = pcie->config_area + config_addr(where,
> +			bus->parent->number == pp->root_bus_nr);
> +retry:
> +	/* Set the config packet devfn */
> +	writel_relaxed(bdf, pp->dbi_base + FUNC0_BDF_NUM);
> +	readl_relaxed(pp->dbi_base + FUNC0_BDF_NUM);
> +
> +	ret = dw_pcie_cfg_read(addr, where, size, &data);
> +
> +	/*
> +	 * This is intended to help with when we are probing the bus. The
> +	 * problem is that the wrapper logic doesn't have any way to
> +	 * interrogate if the configuration request failed or not.
> +	 * On the ARM we actually get a real bus error.
> +	 *
> +	 * Unfortunately this means it is impossible to tell the difference
> +	 * between when a device doesn't exist (the switch will return a UR
> +	 * completion) or the device does exist but isn't yet ready to accept
> +	 * configuration requests (the device will return a CRS completion)

We do have CRS support in the Linux PCI core, so I guess this comment means
that the ST host bridge doesn't handle CRS correctly?

> +	 *
> +	 * The result of this is that we will miss devices when probing.
> +	 *
> +	 * So if we are trying to read the dev/vendor id on devfn 0 and we
> +	 * appear to get zero back, then we retry the request.  We know that
> +	 * zero can never be a valid device/vendor id. The specification says
> +	 * we must retry for up to a second before we decide the device is
> +	 * dead. If we are still dead then we assume there is nothing there and
> +	 * return ~0
> +	 *
> +	 * The downside of this is that we incur a delay of 1s for every pci
> +	 * express link that doesn't have a device connected.

That sounds pretty bad and I assume is a consequence of CRS handling being
broken in hardware.

> +	 */
> +	if (((where & ~3) == 0) && devfn == 0 && (data == 0 || data == ~0)) {
> +		if (retry_count++ < 1000) {
> +			mdelay(1);
> +			goto retry;
> +		} else {
> +			*val = ~0;
> +			return PCIBIOS_DEVICE_NOT_FOUND;
> +		}
> +	}
> +
> +	*val = data;
> +	return ret;
> +}

> +MODULE_LICENSE("GPLv2");

See license_is_gpl_compatible().  This string needs to be "GPL v2", not
"GPLv2" to avoid tainting the kernel.

Bjorn
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