linux-kernel - Re: [PATCH 1/2] [RFC] PCI: read revision ID by default

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Date:	Sat, 09 Jun 2007 12:48:47 -0700
From:	"Kok, Auke" <auke-jan.h.kok@...el.com>
To:	Grant Grundler <grundler@...isc-linux.org>
CC:	linux-kernel@...r.kernel.org, linux-pci@...ey.karlin.mff.cuni.cz,
	gregkh@...e.de
Subject: Re: [PATCH 1/2] [RFC] PCI: read revision ID by default

Grant Grundler wrote:
> On Fri, Jun 08, 2007 at 03:46:30PM -0700, Auke Kok wrote:
>> Currently there are 97 occurrences where drivers need the pci
>> revision ID. We can do this once for all devices. Even the pci
>> subsystem needs the revision several times for quirks. The extra
>> u8 member pads out nicely in the pci_dev struct.
> 
> Good idea. I always wondered why we read the invariants so often
> in the code.
> 
>> Signed-off-by: Auke Kok <auke-jan.h.kok@...el.com>
>> ---
>>
>>  drivers/pci/probe.c |    3 +++
>>  include/linux/pci.h |    1 +
>>  2 files changed, 4 insertions(+), 0 deletions(-)
>>
>> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
>> index e48fcf0..0fdb71d 100644
>> --- a/drivers/pci/probe.c
>> +++ b/drivers/pci/probe.c
>> @@ -918,6 +918,9 @@ pci_scan_device(struct pci_bus *bus, int devfn)
>>  	dev->cfg_size = pci_cfg_space_size(dev);
>>  	dev->error_state = pci_channel_io_normal;
>>  
>> +	/* read the PCI revision: 1 byte */
>> +	pci_read_config_byte(dev, PCI_REVISION_ID, &dev->revision);
> 
> probe.c:pci_setup_device() is also reading this byte but discards it:
> 	pci_read_config_dword(dev, PCI_CLASS_REVISION, &class);
> 	class >>= 8;                                /* upper 3 bytes */
> 	dev->class = class;
> 
> Can you use "class & 0xff"? Or is pci_setup_device() too late?
> Or can you read the whole 32-bits in pci_scan_device() and remove
> the pci_read_config() in pci_setup_device()?

no, pci_setup_device() is just called right after the location where I read the 
REVISION_ID. I'll remove the read and put the dev->revision right after where we 
read the class dword.

Auke
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