On Thu, Mar 18, 2021 at 10:31:43PM +0530, Amey Narkhede wrote: > On 21/03/18 04:57PM, Leon Romanovsky wrote: > > On Thu, Mar 18, 2021 at 07:52:52PM +0530, Amey Narkhede wrote: > > > On 21/03/18 11:09AM, Leon Romanovsky wrote: > > > > On Wed, Mar 17, 2021 at 11:31:40AM -0600, Alex Williamson wrote: > > > > > On Wed, 17 Mar 2021 15:58:40 +0200 > > > > > Leon Romanovsky <leon@xxxxxxxxxx> wrote: <...> > > > > I'm lost here, does vfio-pci use sysfs interface or internal to the kernel API? > > > > > > > > If it is latter then we don't really need sysfs, if not, we still need > > > > some sort of DB to create second policy, because "supported != working". > > > > What am I missing? > > > > > > > > Thanks > > > > > > > Can you explain bit more about why supported != working? > > > > It is written in the commit message of this patch. > > https://lore.kernel.org/lkml/20210312173452.3855-1-ameynarkhede03@xxxxxxxxx/ > > "This feature aims to allow greater control of a device for use cases > > as device assignment, where specific device or platform issues may > > interact poorly with a given reset method, and for which device specific > > quirks have not been developed." > > > > You wrote it and also repeated it a couple of times during the discussion. > > > > If device can understand that specific reset doesn't work, it won't > > perform it in first place. > > > > Thanks > Is it possible for device to understand whether or not specific reset > will work or not prior to performing reset and after it indicates > support for that reset method? Maybe theres problem with that particular > piece of hardware in that machine. > How can database be maintained if a particular machines have > particular piece of faulty HW? It was exactly the reason why I think that VM usecase presented by you is not viable. > If for some reason reset doesn't work it will just give -ENOTTY. > This isn't any different from existing behavior.Actually it informs user > that the reset method didn't reset the device and user can use different > reset method instead of implicitly using different reset method. > If user doesn't explicitly set preferred reset method then > we go ahead with existing implicit fall through behavior which will try all > available reset methods until any one of them works. > If you have device that doesn't support reset at all then you have > option to completely disable it unlike existing reset attribute where > you cannot disable reset. So it gives greater control where you can > disable the reset altogether when quirk isn't developed yet. I explicitly asked to hear usecase, right now, I got an explanation from Alex for policy decision (which doesn't need sysfs) and from you about overcoming HW bugs with expectation that user will be guru of PCI reset methods. > > We can't expect to develop quirk for every device in existence. It doesn't give us an excuse do not try. > For example on my laptop elantech touchpad still doesn't work in 2021 > with vanilla kernel, arch linux applies the patch which was reverted in > mainline kernel for some reason. I see it as a good example of cheap solution. Vendor won't fix your touchpad because distros provide workaround. The same will be with reset. Thanks > > Thanks, > Amey
