linux-kernel - Re: [PATCH v2 1/4] PCI: qcom-ep: Mark BAR0/BAR2 as 64bit BARs and BAR1/BAR3 as RESERVED

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Message-ID: <20241129195537.GA2770926@bhelgaas>
Date: Fri, 29 Nov 2024 13:55:37 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc: kw@...ux.com, gregkh@...uxfoundation.org, arnd@...db.de,
	lpieralisi@...nel.org, shuah@...nel.org, kishon@...nel.org,
	aman1.gupta@...sung.com, p.rajanbabu@...sung.com,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	bhelgaas@...gle.com, linux-arm-msm@...r.kernel.org, robh@...nel.org,
	linux-kselftest@...r.kernel.org, stable+noautosel@...nel.org
Subject: Re: [PATCH v2 1/4] PCI: qcom-ep: Mark BAR0/BAR2 as 64bit BARs and
 BAR1/BAR3 as RESERVED

On Fri, Nov 29, 2024 at 02:54:12PM +0530, Manivannan Sadhasivam wrote:
> On all Qcom endpoint SoCs, BAR0/BAR2 are 64bit BARs by default and software
> cannot change the type. So mark the those BARs as 64bit BARs and also mark
> the successive BAR1/BAR3 as RESERVED BARs so that the EPF drivers cannot
> use them.

"Default" implies an initial setting that can be changed, but you say
"by default" and also "software cannot change the type."  Can they be
anything *other* than 64-bit BARs?

If they're hardwired to be 64-bit BARs, I would just say that.

> Cc: stable+noautosel@...nel.org # depends on patch introducing only_64bit flag

If stable maintainers need to act on this, do they need to search for
the patch introducing only_64bit flag?  That seems onerous; is there a
SHA1 that would make it easier?

> Fixes: f55fee56a631 ("PCI: qcom-ep: Add Qualcomm PCIe Endpoint controller driver")
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> ---
>  drivers/pci/controller/dwc/pcie-qcom-ep.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-qcom-ep.c b/drivers/pci/controller/dwc/pcie-qcom-ep.c
> index e588fcc54589..f925c4ad4294 100644
> --- a/drivers/pci/controller/dwc/pcie-qcom-ep.c
> +++ b/drivers/pci/controller/dwc/pcie-qcom-ep.c
> @@ -823,6 +823,10 @@ static const struct pci_epc_features qcom_pcie_epc_features = {
>  	.msi_capable = true,
>  	.msix_capable = false,
>  	.align = SZ_4K,
> +	.bar[BAR_0] = { .only_64bit = true, },
> +	.bar[BAR_1] = { .type = BAR_RESERVED, },
> +	.bar[BAR_2] = { .only_64bit = true, },
> +	.bar[BAR_3] = { .type = BAR_RESERVED, },
>  };
>  
>  static const struct pci_epc_features *
> -- 
> 2.25.1
>