Re: [PATCH v2 2/4] PCI: brcmstb: Add ACPI config space quirk

["Pali Rohár" <pali@kernel.org>]

On Monday 30 August 2021 11:10:55 Jeremy Linton wrote:
> Hi,
> 
> On 8/29/21 6:13 AM, Pali Rohár wrote:
> > On Thursday 19 August 2021 16:56:53 Jeremy Linton wrote:
> > > The PFTF CM4 is an ACPI platform that isn't ECAM compliant. Its config
> > > space is in two parts. One part is for the root port registers and a
> > > second moveable window pointing at a device's 4K config space. Thus it
> > > doesn't have an MCFG, and any MCFG provided would be nonsense
> > > anyway. Instead, a Linux specific host bridge _DSD selects a custom
> > > ECAM ops and cfgres. The cfg op picks between those two regions while
> > > disallowing problematic accesses.
> > 
> > I'm not sure if Lorenzo would like this patch series...
> 
> That was sorta true since the arm64/ACPI/PCI patches landed. The underlying
> reason is the desire for arm platforms to require less one-off kernel
> patching in order to "just work". But, its become apparent that there
> continue to be problems with PCIe IP and Arm interconnect integration. So, a
> firmware interface was standardized which solves most of the nonstandard
> ECAM issues. At that point it was decided though that the kernel maintainers
> would prefer to have the quirks visible to the kernel rather than hidden in
> the firmware, and that they would be more open to merging these quirks. The
> Tegra patch you listed above has been merged.
> 
> More info about this: https://lkml.org/lkml/2021/3/25/777

Hi and thanks for pointer!

I did not know about that new discussion and a new solution.

Anyway, according to that discussion, adding a new MCFG quirk into
kernel requires adding some errata entry for documenting buggy HW. And
seems that this documentation update is not included in this patch
series...

> 
> Thanks,
> 
> > 
> > In past there was a long discussion about ECAM compliance, MCFG quirks
> > and usage of ACPI (on other platform), see long thread:
> > https://lore.kernel.org/linux-pci/20200207183427.GA40158@google.com/
> > 
> > And I think it is not a good idea to extend MCFG quirks table as
> > according to discussion it was just temporary plaster and if platform is
> > not ACPI / ECAM compliant then it should use DT booting...
> > 
> > Lorenzo, could you put any comment on this?
> > 
> > > Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
> > > ---
> > >   drivers/pci/controller/Makefile            |  1 +
> > >   drivers/pci/controller/pcie-brcmstb-acpi.c | 74 ++++++++++++++++++++++
> > >   include/linux/pci-ecam.h                   |  1 +
> > >   3 files changed, 76 insertions(+)
> > >   create mode 100644 drivers/pci/controller/pcie-brcmstb-acpi.c
> > > 
> > > diff --git a/drivers/pci/controller/Makefile b/drivers/pci/controller/Makefile
> > > index aaf30b3dcc14..65aa6fd3ed89 100644
> > > --- a/drivers/pci/controller/Makefile
> > > +++ b/drivers/pci/controller/Makefile
> > > @@ -57,5 +57,6 @@ ifdef CONFIG_PCI_QUIRKS
> > >   obj-$(CONFIG_ARM64) += pci-thunder-ecam.o
> > >   obj-$(CONFIG_ARM64) += pci-thunder-pem.o
> > >   obj-$(CONFIG_ARM64) += pci-xgene.o
> > > +obj-$(CONFIG_ARM64) += pcie-brcmstb-acpi.o
> > >   endif
> > >   endif
> > > diff --git a/drivers/pci/controller/pcie-brcmstb-acpi.c b/drivers/pci/controller/pcie-brcmstb-acpi.c
> > > new file mode 100644
> > > index 000000000000..71f6def3074c
> > > --- /dev/null
> > > +++ b/drivers/pci/controller/pcie-brcmstb-acpi.c
> > > @@ -0,0 +1,74 @@
> > > +// SPDX-License-Identifier: GPL-2.0+
> > > +/*
> > > + * ACPI quirks for Brcm2711 PCIe host controller
> > > + * As used on the Raspberry Pi Compute Module 4
> > > + *
> > > + * Copyright (C) 2021 Arm Ltd.
> > > + */
> > > +
> > > +#include <linux/io.h>
> > > +#include <linux/pci.h>
> > > +#include <linux/pci-ecam.h>
> > > +#include "../pci.h"
> > > +#include "pcie-brcmstb.h"
> > > +
> > > +static int brcm_acpi_init(struct pci_config_window *cfg)
> > > +{
> > > +	/*
> > > +	 * This platform doesn't technically have anything that could be called
> > > +	 * ECAM. Its config region has root port specific registers between
> > > +	 * standard PCIe defined config registers. Thus the region setup by the
> > > +	 * generic ECAM code needs to be adjusted. The HW can access bus 0-ff
> > > +	 * but the footprint isn't a nice power of 2 (40k). For purposes of
> > > +	 * mapping the config region we are just going to squash the standard
> > > +	 * and nonstandard registers together rather than mapping them separately.
> > > +	 */
> > > +	iounmap(cfg->win);
> > > +	cfg->win = pci_remap_cfgspace(cfg->res.start, resource_size(&cfg->res));
> > > +	if (!cfg->win)
> > > +		goto err_exit;
> > > +
> > > +	/* MSI is nonstandard as well */
> > > +	pci_no_msi();
> > > +
> > > +	return 0;
> > > +err_exit:
> > > +	dev_err(cfg->parent, "PCI: Failed to remap config\n");
> > > +	return -ENOMEM;
> > > +}
> > > +
> > > +static void __iomem *brcm_pcie_map_conf2(struct pci_bus *bus,
> > > +					unsigned int devfn, int where)
> > > +{
> > > +	struct pci_config_window *cfg = bus->sysdata;
> > > +	void __iomem *base = cfg->win;
> > > +	int idx;
> > > +	u32 up;
> > > +
> > > +	/* Accesses to the RC go right to the RC registers if slot==0 */
> > > +	if (pci_is_root_bus(bus))
> > > +		return PCI_SLOT(devfn) ? NULL : base + where;
> > > +
> > > +	/* Assure link up before sending request */
> > > +	up = readl(base + PCIE_MISC_PCIE_STATUS);
> > > +	if (!(up & PCIE_MISC_PCIE_STATUS_PCIE_DL_ACTIVE_MASK))
> > > +		return NULL;
> > > +
> > > +	if (!(up & PCIE_MISC_PCIE_STATUS_PCIE_PHYLINKUP_MASK))
> > > +		return NULL;
> > > +
> > > +	/* For devices, write to the config space index register */
> > > +	idx = PCIE_ECAM_OFFSET(bus->number, devfn, 0);
> > > +	writel(idx, base + PCIE_EXT_CFG_INDEX);
> > > +	return base + PCIE_EXT_CFG_DATA + where;
> > > +}
> > > +
> > > +const struct pci_ecam_ops bcm2711_pcie_ops = {
> > > +	.init		= brcm_acpi_init,
> > > +	.bus_shift	= 1,
> > > +	.pci_ops	= {
> > > +		.map_bus	= brcm_pcie_map_conf2,
> > > +		.read		= pci_generic_config_read,
> > > +		.write		= pci_generic_config_write,
> > > +	}
> > > +};
> > > diff --git a/include/linux/pci-ecam.h b/include/linux/pci-ecam.h
> > > index adea5a4771cf..a5de0285bb7f 100644
> > > --- a/include/linux/pci-ecam.h
> > > +++ b/include/linux/pci-ecam.h
> > > @@ -87,6 +87,7 @@ extern const struct pci_ecam_ops xgene_v1_pcie_ecam_ops; /* APM X-Gene PCIe v1 *
> > >   extern const struct pci_ecam_ops xgene_v2_pcie_ecam_ops; /* APM X-Gene PCIe v2.x */
> > >   extern const struct pci_ecam_ops al_pcie_ops;	/* Amazon Annapurna Labs PCIe */
> > >   extern const struct pci_ecam_ops tegra194_pcie_ops; /* Tegra194 PCIe */
> > > +extern const struct pci_ecam_ops bcm2711_pcie_ops; /* Bcm2711 PCIe */
> > >   #endif
> > >   #if IS_ENABLED(CONFIG_PCI_HOST_COMMON)
> > > -- 
> > > 2.31.1
> > > 
>