reprobing BAR sizes and capabilities after a FLR?

reprobing BAR sizes and capabilities after a FLR?

[Christoph Hellwig]

Hi all,

I've just been talking to some firmware developers that were a little
surprised that Linux does not reprobe BAR sizes after a FLR.  I looked
at our code and we do not reprobe anything at all after a FLR.  Is it
a good assumption that a devices comes back in exactly the same state
after an FLR?

Re: reprobing BAR sizes and capabilities after a FLR?

[Sinan Kaya]

On 7/9/2019 11:40 AM, Christoph Hellwig wrote:
> Hi all,
> 
> I've just been talking to some firmware developers that were a little
> surprised that Linux does not reprobe BAR sizes after a FLR.  I looked
> at our code and we do not reprobe anything at all after a FLR.  Is it
> a good assumption that a devices comes back in exactly the same state
> after an FLR?
> 

What's the use case for BAR size changing? I do remember that code was
saving the assigned BAR values.

I don't think FLR can be treated as a full enumeration.

Re: reprobing BAR sizes and capabilities after a FLR?

[Bjorn Helgaas]

[+cc Alex]

On Tue, Jul 09, 2019 at 08:40:19AM -0700, Christoph Hellwig wrote:
> Hi all,
> 
> I've just been talking to some firmware developers that were a little
> surprised that Linux does not reprobe BAR sizes after a FLR.  I looked
> at our code and we do not reprobe anything at all after a FLR.  Is it
> a good assumption that a devices comes back in exactly the same state
> after an FLR?

I am a little nervous about the fact that we don't reprobe devices
after reset because the reset may cause the device to load new
firmware, which may cause arbitrary changes (device type, number and
size of BARs, etc).  FLR is a little more restrictive than
Conventional Reset, e.g., FLR must not affect the link state, so maybe
it's safer to assume BAR sizes are unchanged.  But I'm not at all
confident about that.

I mooted the idea of reprobing after reset, but that would break higher
level software that isn't prepared to see hotplug-like events caused by
reset, so haven't gone that direction (yet).

Bjorn