linux-kernel - Re: [RFC PATCH v4 3/5] PCI: Check platform specific ECAM quirks

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Date:	Wed, 29 Jun 2016 12:48:19 +0200
From:	Tomasz Nowicki <tn@...ihalf.com>
To:	Duc Dang <dhdang@....com>,
	Christopher Covington <cov@...eaurora.org>
Cc:	Bjorn Helgaas <helgaas@...nel.org>, Arnd Bergmann <arnd@...db.de>,
	Will Deacon <will.deacon@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Rafael Wysocki <rafael@...nel.org>,
	Hanjun Guo <hanjun.guo@...aro.org>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Sinan Kaya <okaya@...eaurora.org>,
	Jayachandran C <jchandra@...adcom.com>,
	Robert Richter <robert.richter@...iumnetworks.com>,
	Marcin Wojtas <mw@...ihalf.com>,
	Liviu Dudau <Liviu.Dudau@....com>,
	David Daney <ddaney@...iumnetworks.com>,
	Yijing Wang <wangyijing@...wei.com>,
	Mark Salter <msalter@...hat.com>, linux-pci@...r.kernel.org,
	linux-arm <linux-arm-kernel@...ts.infradead.org>,
	linux-acpi@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linaro-acpi@...ts.linaro.org, Jon Masters <jcm@...hat.com>,
	Andrea Gallo <andrea.gallo@...aro.org>, jeremy.linton@....com,
	Dongdong Liu <liudongdong3@...wei.com>,
	Gabriele Paoloni <gabriele.paoloni@...wei.com>,
	Jeffrey Hugo <jhugo@...eaurora.org>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>
Subject: Re: [RFC PATCH v4 3/5] PCI: Check platform specific ECAM quirks

On 28.06.2016 18:12, Duc Dang wrote:
> On Tue, Jun 28, 2016 at 6:04 AM, Christopher Covington
> <cov@...eaurora.org> wrote:
>> Hi Tomasz,
>>
>> On 06/28/2016 03:54 AM, Tomasz Nowicki wrote:
>>
>>> diff --git a/drivers/pci/host/mcfg-quirks.c b/drivers/pci/host/mcfg-quirks.c
>>> new file mode 100644
>>> index 0000000..fb2b184
>>> --- /dev/null
>>> +++ b/drivers/pci/host/mcfg-quirks.c
>>> @@ -0,0 +1,88 @@
>>
>>> +static bool pci_mcfg_fixup_match(struct pci_cfg_fixup *f,
>>> +                              struct acpi_table_header *mcfg_header)
>>> +{
>>> +     int olen = min_t(u8, strlen(f->oem_id), ACPI_OEM_ID_SIZE);
>>> +     int tlen = min_t(u8, strlen(f->oem_table_id), ACPI_OEM_TABLE_ID_SIZE);
>>> +
>>> +     return (!strncmp(f->oem_id, mcfg_header->oem_id, olen) &&
>>> +             !strncmp(f->oem_table_id, mcfg_header->oem_table_id, tlen) &&
>>> +             f->oem_revision == mcfg_header->oem_revision);
>>> +}
>>
>> Ard's comments on v3 included:
>>
>> "... exact OEM table/rev id matches ..."
>> "... substring match ... out of the question ..."
>>
>> I originally advocated the substring match approach because
>> space-padding the input strings was unfamiliar. But given that some
>> vendors have a "PLAT    " then "PLAT2   " naming scheme, where the
>> former needs quirks and the latter (hopefully) doesn't, I agree with Ard
>> and think space-padded inputs is the better way to go. Sorry for the
>> lack of foresight.
>
> I think having OEM Table ID as "PLAT   " and then "PLAT2  " (the the
> next version of the SoC)
> is common. So yes, matching full string is better as we can use "PLAT2  "
> in MCFG table and not worry about the "PLAT" sub-string match causes the quirk
> to be applied unintentionally.
>

Sorry, I forgot to address Ard's comment.

Note that platforms already shipped where OEM string has no padding will 
have change the firmware or add 0 padding to our quirk array IDs.
So how about:

static bool pci_mcfg_fixup_match(struct pci_cfg_fixup *f,
				 struct acpi_table_header *mcfg_header)
{
	int olen = strnlen(mcfg_header->oem_id, ACPI_OEM_ID_SIZE);
	int tlen = strnlen(mcfg_header->oem_table_id, ACPI_OEM_TABLE_ID_SIZE);

	if (olen != strlen(f->oem_id) || tlen != strlen(f->oem_table_id))
		return false;

	return (!strncmp(f->oem_id, mcfg_header->oem_id, olen) &&
		!strncmp(f->oem_table_id, mcfg_header->oem_table_id, tlen) &&
		f->oem_revision == mcfg_header->oem_revision);
}

This should work for all cases:
1. "PLAT"
2. "PLAT    " padding
3. No need to change existing firmware

Tomasz