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

[Jeremy Linton <jeremy.linton@arm.com>]

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


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
>>