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SubjectRe: [RFC 1/3] PCI: pci-driver: Introduce pci device delete list
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Hi Greg,

On 09/28/2017 03:09 AM, Greg Kroah-Hartman wrote:
> On Wed, Sep 27, 2017 at 04:40:20PM -0400, Jon Derrick wrote:
>> This patch introduces a new kernel command line parameter to mask pci
>> device ids from pci driver id tables. This prevents masked devices from
>> automatically binding to both built-in and module drivers.
>>
>> Devices can be later attached through the driver's sysfs new_id
>> inteface.
>>
>> The use cases for this are primarily for debugging, eg, being able to
>> prevent attachment before probes are set up. It can also be used to mask
>> off faulty built-in hardware or faulty simulated hardware.
>>
>> Another use case is to prevent attachment of devices which will be
>> passed to VMs, shortcutting the detachment effort.
>
> Is the "shortcut" really that big of a deal? unbind actually causes
> problems? Is this an attempt to deal with devices being handled by more
> than one driver and then you want to manually bind it later on?
>
>> The format is similar to the sysfs new_id format. Device ids are
>> specified with:
>>
>> VVVV:DDDD[:SVVV:SDDD][:CCCC][:MMMM]
>>
>> Where:
>> VVVV = Vendor ID
>> DDDD = Device ID
>> SVVV = Subvendor ID
>> SDDD = Subdevice ID
>> CCCC = Class
>> MMMM = Class Mask
>>
>> IDs can be chained with commas.
>>
>> Examples:
>> <driver>.delete_id=1234:5678
>> <driver>.delete_id=ffffffff:ffffffff
>> <driver>.delete_id=ffffffff:ffffffff:ffffffff:ffffffff:010802
>> <driver>.delete_id=1234:5678,abcd:ef01,2345:ffffffff
>
> What about drivers that handle more than one bus type (i.e. USB and
> PCI?) This format is specific to PCI, yet you are defining it as a
> "global" for all drivers :(
>
I was hoping to extend it to other bus types as well, but just wanted
some early feedback on the idea. Pci was the easier implementation for
me. Could prepending pci:, usb:, etc on the format be an option?

> This feels hacky, what is the real reason for this? It feels like we
> have so many different ways to blacklist and unbind and bind devices to
> drivers already, why add yet-another way?
>
I ran into an issue a while back where I needed to disable a device from
a built-in driver to perform a regression test. I worked around that
issue by doing an initcall_blacklist on the pci-driver declaration, but
that also preventing later binding because the driver was never registered.

I've also had issues with remote systems where pluggable devices were
broken or otherwise non-responsive, and it would have been nice to have
been able to keep them from binding on module loading as a temporary
workaround until someone could have removed those devices (though
impossible on built-in hardware).

I'm not sure about hacky; I think the implementation in this patch (1/3)
is pretty clean :). I'm not familiar with all the different ways of
blacklisting. Is there another way to work around the issues I listed above?

I understand the concern about having it exist in the format <driver>.
and only supporting one or a few bus types. I have another set that
extends the pci= parameter instead.

> thanks,
>
> greg k-h
>

Best,
Jon

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