Re: [PATCH] PCI: dwc: ep: Enforce DWC specific 64-bit BAR limitiation

[Manivannan Sadhasivam <mani@kernel.org>]

On Tue, May 28, 2024 at 03:48:40PM +0200, Niklas Cassel wrote:
> From the DWC EP databook 5.96a, section "3.5.7.1.4 General Rules for BAR
> Setup (Fixed Mask or Programmable Mask Schemes Only)":
> 
> "Any pair (for example BARs 0 and 1) can be configured as one 64-bit BAR,
> two 32-bit BARs, or one 32-bit BAR."
> 
> "BAR pairs cannot overlap to form a 64-bit BAR. For example, you cannot
> combine BARs 1 and 2 to form a 64-bit BAR."
> 
> While this limitation does exist in some other PCI endpoint controllers,
> e.g. cdns_pcie_ep_set_bar(), the limitation does not appear to be defined
> in the PCIe specification itself, thus add an explicit check for this in
> dw_pcie_ep_set_bar() (rather than pci_epc_set_bar()).
> 
> Signed-off-by: Niklas Cassel <cassel@kernel.org>

Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>

- Mani

> ---
>  drivers/pci/controller/dwc/pcie-designware-ep.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-designware-ep.c b/drivers/pci/controller/dwc/pcie-designware-ep.c
> index f22252699548..42db3c3bbe96 100644
> --- a/drivers/pci/controller/dwc/pcie-designware-ep.c
> +++ b/drivers/pci/controller/dwc/pcie-designware-ep.c
> @@ -227,6 +227,13 @@ static int dw_pcie_ep_set_bar(struct pci_epc *epc, u8 func_no, u8 vfunc_no,
>  	int ret, type;
>  	u32 reg;
>  
> +	/*
> +	 * DWC does not allow BAR pairs to overlap, e.g. you cannot combine BARs
> +	 * 1 and 2 to form a 64-bit BAR.
> +	 */
> +	if ((flags & PCI_BASE_ADDRESS_MEM_TYPE_64) && (bar & 1))
> +		return -EINVAL;
> +
>  	reg = PCI_BASE_ADDRESS_0 + (4 * bar);
>  
>  	if (!(flags & PCI_BASE_ADDRESS_SPACE))
> -- 
> 2.45.1
> 

-- 
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