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Message-ID: <20150112184349.GB2776@google.com>
Date: Mon, 12 Jan 2015 11:43:49 -0700
From: Bjorn Helgaas <bhelgaas@...gle.com>
To: Gabriel FERNANDEZ <gabriel.fernandez@...com>
Cc: Rob Herring <robh+dt@...nel.org>, Pawel Moll <pawel.moll@....com>,
Mark Rutland <mark.rutland@....com>,
Ian Campbell <ijc+devicetree@...lion.org.uk>,
Kumar Gala <galak@...eaurora.org>,
Srinivas Kandagatla <srinivas.kandagatla@...il.com>,
Maxime Coquelin <maxime.coquelin@...com>,
Patrice Chotard <patrice.chotard@...com>,
Russell King <linux@....linux.org.uk>,
Mohit Kumar <mohit.kumar@...com>,
Jingoo Han <jg1.han@...sung.com>,
Grant Likely <grant.likely@...aro.org>,
Gabriel Fernandez <gabriel.fernandez@...aro.org>,
Fabrice Gasnier <fabrice.gasnier@...com>,
Arnd Bergmann <arnd@...db.de>,
Viresh Kumar <viresh.kumar@...aro.org>,
Thierry Reding <treding@...dia.com>,
Minghuan Lian <Minghuan.Lian@...escale.com>,
Magnus Damm <damm@...nsource.se>,
Will Deacon <will.deacon@....com>,
Tanmay Inamdar <tinamdar@....com>,
Murali Karicheri <m-karicheri2@...com>,
Kishon Vijay Abraham I <kishon@...com>,
Pratyush Anand <pratyush.anand@...com>,
Sachin Kamat <sachin.kamat@...sung.com>,
Andrew Lunn <andrew@...n.ch>,
Liviu Dudau <Liviu.Dudau@....com>,
Srikanth Thokala <sthokal@...inx.com>,
devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org, kernel@...inux.com,
linux-pci@...r.kernel.org, Lee Jones <lee.jones@...aro.org>
Subject: Re: [PATCH 3/5] PCI: st: Provide support for the sti PCIe controller
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@...com>
> Signed-off-by: Gabriel Fernandez <gabriel.fernandez@...aro.org>
> ---
> 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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