linux-kernel - Re: [PATCH] PCI: endpoint: pci-epf-test: Limit PCIe BAR size for fixed BARs

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Message-ID: <62584e30-72ab-49df-bfaa-9730679b2dbe@mailbox.org>
Date: Thu, 4 Sep 2025 23:29:15 +0200
From: Marek Vasut <marek.vasut@...lbox.org>
To: Niklas Cassel <cassel@...nel.org>, Damien Le Moal <dlemoal@...nel.org>
Cc: Marek Vasut <marek.vasut+renesas@...lbox.org>, linux-pci@...r.kernel.org,
 Krzysztof Wilczyński <kwilczynski@...nel.org>,
 Bjorn Helgaas <bhelgaas@...gle.com>, Frank Li <Frank.Li@....com>,
 Kishon Vijay Abraham I <kishon@...nel.org>,
 Manivannan Sadhasivam <mani@...nel.org>, Wang Jiang <jiangwang@...inos.cn>,
 linux-kernel@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
 Jerome Brunet <jbrunet@...libre.com>
Subject: Re: [PATCH] PCI: endpoint: pci-epf-test: Limit PCIe BAR size for
 fixed BARs

On 9/4/25 2:28 PM, Niklas Cassel wrote:

Hello Niklas,

[...]

> pci_epf_alloc_space() works like this:
> If the user requests a BAR size that is smaller than the fixed-size BAR,
> it will allocate space matching the fixed-size.
> 
> As in most cases, having a BAR larger than needed by an EPF driver is
> still acceptable.
> 
> However, if the user requests a size larger than the fixed-size BAR,
> as in your case, we will return an error, as we cannot fulfill the
> user's request.
> 
> I don't see any alternative other than your/Damien's proposal above.
> 
> Unfortunately, all EPF drivers would probably need this same change.

It seems that pci-epf-ntb and pci-epf-vntb only use BAR0 (BAR_CONFIG) 
and BAR0+BAR1 (BAR_CONFIG and BAR_DB) , so those should be OK on this 
controller. NVMe EPF also seems to use only BAR0 and it specifically 
handles fixed size BAR. It seems everything that is in the tree so far 
managed to sidestep hitting fixed-size BAR4 problems on this hardware, 
except for the test driver.