linux-kernel - Re: [PATCH v4 3/3] vfio/nvgrace-gpu: Check the HBM training and C2C link status

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Message-ID:
 <SA1PR12MB7199E9E9C53B987709CCB849B0E72@SA1PR12MB7199.namprd12.prod.outlook.com>
Date: Mon, 20 Jan 2025 03:35:22 +0000
From: Ankit Agrawal <ankita@...dia.com>
To: Alex Williamson <alex.williamson@...hat.com>
CC: Jason Gunthorpe <jgg@...dia.com>, Yishai Hadas <yishaih@...dia.com>,
	"shameerali.kolothum.thodi@...wei.com"
	<shameerali.kolothum.thodi@...wei.com>, "kevin.tian@...el.com"
	<kevin.tian@...el.com>, Zhi Wang <zhiw@...dia.com>, Aniket Agashe
	<aniketa@...dia.com>, Neo Jia <cjia@...dia.com>, Kirti Wankhede
	<kwankhede@...dia.com>, "Tarun Gupta (SW-GPU)" <targupta@...dia.com>, Vikram
 Sethi <vsethi@...dia.com>, Andy Currid <acurrid@...dia.com>, Alistair Popple
	<apopple@...dia.com>, John Hubbard <jhubbard@...dia.com>, Dan Williams
	<danw@...dia.com>, "Anuj Aggarwal (SW-GPU)" <anuaggarwal@...dia.com>, Matt
 Ochs <mochs@...dia.com>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 3/3] vfio/nvgrace-gpu: Check the HBM training and C2C
 link status

> No, this is standard PCI driver stuff, everything you need is already
> there.  Probably pci_enable_device() and some variant of
> pci_request_regions().

Ok thanks, I'll take a look at that.

>> > > Does this delay even need to happen in the probe function, or could it
>> > > happen in the open_device callback?  That would still be before user
>> > > access, but if we expect it to generally work, it would allow the
>> > > training to happen in the background up until the user tries to open
>> > > the device.  Thanks,
>> > >
>> > > Alex
>> >
>> > The thought process is that since it is purely bare metal coming to proper
>> > state while boot, the nvgrace module should probably wait for the startup
>> > to complete during probe() instead of delaying until open() time.
>>
>> If the driver is statically loaded, that might mean you're willing to
>> stall boot for up to 30s.  In practice is this ever actually going to
>> fail?  Thanks,

No, I have not seen this getting timeout in my testing. 30s is considered
to be sufficient to be sure that the hardware is not in a bad state.

> On second thought, I guess a vfio-pci variant driver can't
> automatically bind to a device, whether statically built or not, so
> maybe this isn't a concern.  I'm not sure if there are other concerns
> with busy waiting for up to 30s at driver probe.  Thanks,
>
> Alex