Re: [PATCH v2 7/9] PCI: cadence: Set a 64-bit BAR if requested

[Bjorn Helgaas <helgaas@kernel.org>]

[+cc Shawn for Rockchip question]

On Tue, Mar 12, 2024 at 11:51:47AM +0100, Niklas Cassel wrote:
> Ever since commit f25b5fae29d4 ("PCI: endpoint: Setting a BAR size > 4 GB
> is invalid if 64-bit flag is not set") it has been impossible to get the
> .set_bar() callback with a BAR size > 4 GB, if the BAR was also not
> requested to be configured as a 64-bit BAR.
> 
> Thus, forcing setting the 64-bit flag for BARs larger than 4 GB in the
> lower level driver is dead code and can be removed.
> 
> It is however possible that an EPF driver configures a BAR as 64-bit,
> even if the requested size is < 4 GB.
> 
> Respect the requested BAR configuration, just like how it is already
> repected with regards to the prefetchable bit.
> 
> Signed-off-by: Niklas Cassel <cassel@kernel.org>
> ---
>  drivers/pci/controller/cadence/pcie-cadence-ep.c | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
> 
> diff --git a/drivers/pci/controller/cadence/pcie-cadence-ep.c b/drivers/pci/controller/cadence/pcie-cadence-ep.c
> index 2d0a8d78bffb..de10e5edd1b0 100644
> --- a/drivers/pci/controller/cadence/pcie-cadence-ep.c
> +++ b/drivers/pci/controller/cadence/pcie-cadence-ep.c
> @@ -99,14 +99,11 @@ static int cdns_pcie_ep_set_bar(struct pci_epc *epc, u8 fn, u8 vfn,
>  		ctrl = CDNS_PCIE_LM_BAR_CFG_CTRL_IO_32BITS;
>  	} else {
>  		bool is_prefetch = !!(flags & PCI_BASE_ADDRESS_MEM_PREFETCH);
> -		bool is_64bits = sz > SZ_2G;
> +		bool is_64bits = !!(flags & PCI_BASE_ADDRESS_MEM_TYPE_64);
>  
>  		if (is_64bits && (bar & 1))
>  			return -EINVAL;

Not relevant to *this* patch, but it looks like this code assumes that
a 64-bit BAR must consist of an even-numbered DWORD followed by an
odd-numbered one, e.g., it could be BAR 0 and BAR 1, but not BAR 1 and
BAR 2.

I don't think the PCIe spec requires that.  Does the Cadence hardware
require this?

What about Rockchip, which has similar code in
rockchip_pcie_ep_set_bar()?

FWIW, dw_pcie_ep_set_bar() doesn't enforce this restriction.

> -		if (is_64bits && !(flags & PCI_BASE_ADDRESS_MEM_TYPE_64))
> -			epf_bar->flags |= PCI_BASE_ADDRESS_MEM_TYPE_64;
> -
>  		if (is_64bits && is_prefetch)
>  			ctrl = CDNS_PCIE_LM_BAR_CFG_CTRL_PREFETCH_MEM_64BITS;
>  		else if (is_prefetch)
> -- 
> 2.44.0
>