Re: [PATCH v2 2/3] PCI: tegra194: Reset BARs when running in PCIe endpoint mode

[Niklas Cassel <cassel@kernel.org>]

On Tue, Feb 10, 2026 at 04:09:05PM +0530, Manikanta Maddireddy wrote:
> > For pci-keystone.c, this is the only driver that is a bit weird, it marks
> > BAR0 and BAR1 as reserved, but does not disable them in the init() callback.
> > It seems force set BAR0 as a 32-bit BAR in the init() callback.
> > 
> > Thus, for all drivers except for pci-keystone.c, BAR_RESERVED does mean
> > BAR_DISABLED. Feel free to send a patch that renames BAR_RESERVED to
> > BAR_DISABLED.
> > 
> > If you send such a patch, perhaps you also want to modify the PCI endpoint
> > core to call reset_bar() for all BARs marked as BAR_RESERVED/BAR_DISABLED,
> > instead of each EPC driver doing so in the init() callback. I think the main
> > reason why this is not done already is that thare is no reset_bar() op in
> > struct pci_epc_ops epc_ops, there is only clear_bar() which clears an BAR
> > enabled by an EPF driver. (So you would most likely also need to add a
> > .disable_bar() op in struct pci_epc_ops epc_ops.)
> > 
> pci-epc.h defined
> 
>  * @BAR_RESERVED: The BAR should not be touched by an EPF driver.
> 
> I believe you are interpreting this as unused BAR?
> 
> In Tegra PCIe, BAR2 and BAR4 are backed by PCIe HW memory which
> 
> shouldn't be touched by EPF, but should be kept enabled.
> 
> This support is not available. I suggested to add BAR_DISABLED
> 
> for unused and use BAR_RESERVED for bars like above.

I understand what you want. You want to have a BAR_RESERVED and a
BAR_DISABLED.

Sounds like a nice feature. Feel free to add that.


But like I mentioned in my reply, for all existing drivers, except for
pci-keystone.c, in practice BAR_RESERVED actually means BAR_DISABLED.
(Since all drivers except for pci-keystone.c call reset_bar() in init(),
and pci-epf-test will not enable BARs marked as BAR_RESERVED).

So if you add a BAR_DISABLED, make sure that you convert all existing
uses of BAR_RESERVED (except for pci-keystone.c) to BAR_DISABLED.

pci-keystone.c and pcie-tegra194.c can then be the only drivers that
have BARs marked as BAR_RESERVED (all other drivers would use BAR_DISABLED).

Please just make sure that you don't regress the amount of currently passing
pci_endpoint_test test cases that are passing for pcie-tegra194.c.
(Which would be the case if you revert the patch in $subject without first
adding your proposed new BAR_DISABLED, such that we can have a distinction
between BAR_DISABLED and BAR_RESERVED.)


Kind regards,
Niklas