Re: [PATCH v3 3/4] PCI/ACPI: Add Broadcom bcm2711 MCFG quirk

From: "Pali Rohár" <pali@kernel.org>
To: bhelgaas@google.com, Jeremy Linton <jeremy.linton@arm.com>
Cc: linux-pci@vger.kernel.org, lorenzo.pieralisi@arm.com,
	nsaenz@kernel.org, bhelgaas@google.com, rjw@rjwysocki.net,
	lenb@kernel.org, robh@kernel.org, kw@linux.com,
	f.fainelli@gmail.com, bcm-kernel-feedback-list@broadcom.com,
	linux-acpi@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	linux-rpi-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 3/4] PCI/ACPI: Add Broadcom bcm2711 MCFG quirk
Date: Tue, 5 Oct 2021 22:02:27 +0200	[thread overview]
Message-ID: <20211005200227.ltl6owwksfn7l4xx@pali> (raw)
In-Reply-To: <20210826071557.29239-4-jeremy.linton@arm.com>

On Thursday 26 August 2021 02:15:56 Jeremy Linton wrote:
> Now that there is a bcm2711 quirk, it needs to be enabled when the
> MCFG is missing. Use an ACPI namespace _DSD property
> "linux-ecam-quirk-id" as an alternative to the MCFG OEM.
> 
> Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
> Acked-by: Florian Fainelli <f.fainelli@gmail.com>
> Acked-by: Bjorn Helgaas <bhelgaas@google.com>
> ---
>  drivers/acpi/pci_mcfg.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/drivers/acpi/pci_mcfg.c b/drivers/acpi/pci_mcfg.c
> index 53cab975f612..04c517418365 100644
> --- a/drivers/acpi/pci_mcfg.c
> +++ b/drivers/acpi/pci_mcfg.c
> @@ -169,6 +169,9 @@ static struct mcfg_fixup mcfg_quirks[] = {
>  	ALTRA_ECAM_QUIRK(1, 13),
>  	ALTRA_ECAM_QUIRK(1, 14),
>  	ALTRA_ECAM_QUIRK(1, 15),
> +
> +	{ "bc2711", "", 0, 0, MCFG_BUS_ANY, &bcm2711_pcie_ops,
> +	  DEFINE_RES_MEM(0xFD500000, 0xA000) },

Hello!

According to discussion described in email [1], adding a new MCFG quirk
(like above) into kernel requires adding some errata entry for
documenting buggy HW.

But this patch series does not introduce any new errata entry.

Bjorn, could you look at how to properly document these "hw bugs"?
I guess there would be lot of more requests for adding MCFG quirks as
now according to [1], doors are open for them. And it is possible that
after more years nobody would be able to maintain these quirks if would
not be properly documented.

[1] - https://lore.kernel.org/linux-pci/20210325131231.GA18590@e121166-lin.cambridge.arm.com/

>  };
>  
>  static char mcfg_oem_id[ACPI_OEM_ID_SIZE];
> @@ -198,8 +201,22 @@ static void pci_mcfg_apply_quirks(struct acpi_pci_root *root,
>  	u16 segment = root->segment;
>  	struct resource *bus_range = &root->secondary;
>  	struct mcfg_fixup *f;
> +	const char *soc;
>  	int i;
>  
> +	/*
> +	 * This may be a machine with a PCI/SMC conduit, which means it doesn't
> +	 * have an MCFG. Use an ACPI namespace definition instead.
> +	 */
> +	if (!fwnode_property_read_string(acpi_fwnode_handle(root->device),
> +					 "linux-ecam-quirk-id", &soc)) {
> +		if (strlen(soc) != ACPI_OEM_ID_SIZE)
> +			dev_err(&root->device->dev, "ECAM quirk should be %d characters\n",
> +				ACPI_OEM_ID_SIZE);
> +		else
> +			memcpy(mcfg_oem_id, soc, ACPI_OEM_ID_SIZE);
> +	}
> +
>  	for (i = 0, f = mcfg_quirks; i < ARRAY_SIZE(mcfg_quirks); i++, f++) {
>  		if (pci_mcfg_quirk_matches(f, segment, bus_range)) {
>  			if (f->cfgres.start)
> -- 
> 2.31.1
> 