Re: [RFC PATCH 1/2] PCI: Add pci=hpreserve= to reserve memory windows for a hotplug bridge

[sashiko-bot@kernel.org]

> A hotplug bridge is sized for the devices that are present when its
> windows are sized, plus the optional hpmmiosize/hpmmioprefsize space.
> Some topologies have devices that are known to appear later.  After a
> reset of a two-level PCIe switch hierarchy, for example, pciehp
> re-enumerates the upstream switch before the link to the nested switch
> is back up, so the downstream port leading to the nested switch is
> sized with nothing below it.  When the nested switch appears, its BARs
> do not fit.
> 
> On a two-level Microchip PM50052 (Switchtec PFX) hierarchy whose nested
> switch has an NTB function with a 1 GiB prefetchable BAR, a hard reset
> of the top-level switch on v7.3-rc2 leaves downstream port 82:03.0
> with a 206 MiB prefetchable window, an equal share of its
> parent's window.  The nested switch returns about 0.6 s later and
> fails:
> [ ... ]
> 
> Without the parameter nothing changes.
> 
> Tested-by: Maciej Grochowski <maciej.grochowski@sony.com>
> Signed-off-by: Maciej Grochowski <maciej.grochowski@sony.com>

Sashiko has reviewed this patch and found no issues. It looks great!

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261002193111.51637-1-maciej.grochowski@sony.com?part=1