From: Niklas Cassel <cassel@kernel.org>
To: Manikanta Maddireddy <mmaddireddy@nvidia.com>
Cc: mani@kernel.org, kwilczynski@kernel.org,
linux-pci@vger.kernel.org, kishon@kernel.org,
Frank.Li@kernel.org, bhelgaas@google.com, den@valinux.co.jp,
thierry.reding@kernel.org, jonathanh@nvidia.com,
vidyas@nvidia.com, linux-tegra@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v1] PCI: endpoint: Skip upper halves of 64-bit BARs during search
Date: Wed, 21 Oct 2026 16:25:34 +0200 [thread overview]
Message-ID: <atjLXvkc-XZNF0oi@ryzen> (raw)
In-Reply-To: <atiX5UoJ0qgV0wGN@ryzen>
On Wed, Oct 21, 2026 at 12:46:03PM +0200, Niklas Cassel wrote:
> On Wed, Oct 21, 2026 at 01:36:44PM +0530, Manikanta Maddireddy wrote:
> > pci_epc_get_next_free_bar() skips the upper half of a 64-bit BAR only
> > when it is the starting BAR. If the search subsequently passes a
> > reserved or disabled 64-bit BAR, it can return its upper half as an
> > independent BAR because that slot has a default programmable descriptor.
> >
> > For example, Tegra exposes a programmable 64-bit BAR0 and reserved
> > 64-bit BAR2 and BAR4. A search starting at BAR1 skips BAR1 and BAR2,
> > then incorrectly returns BAR3. The next search can similarly return
> > BAR5, causing the EPF test driver to allocate and program BARs that
> > belong to the reserved hardware windows.
>
> 12a22fb38cbb ("PCI: tegra194: Expose BAR2 (MSI-X) and BAR4 (DMA) as
> 64-bit BAR_RESERVED").
>
>
> I'm fine with this patch, but I think you need to rephrase the kdoc
> to reflect this new reality, because currently the kdoc is confusing/
> not in line with the 'new' meaning of BAR_RESERVED, which can contain
> MSI-X table etc.
To clarify, I can see that you updated the definition in:
27ce1d8ecb9b ("PCI: endpoint: Allow only_64bit on BAR_RESERVED")
But, IMO it is still not super clear.
Perhaps we should have mentioned explicitly that only_64bit is
also allowed on a BAR_RESERVED, if that reserved BAR is 64-bit.
(Since that use case is different from what the kdoc currently
says.)
I also think that this patch needs a Fixes tag with either:
27ce1d8ecb9b ("PCI: endpoint: Allow only_64bit on BAR_RESERVED")
or
12a22fb38cbb ("PCI: tegra194: Expose BAR2 (MSI-X) and BAR4 (DMA) as
64-bit BAR_RESERVED")
Kind regards,
Niklas
prev parent reply other threads:[~2026-10-21 14:25 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-21 8:06 Manikanta Maddireddy
2026-10-21 10:45 ` Niklas Cassel
2026-10-21 14:25 ` Niklas Cassel [this message]
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