linux-kernel - Re: [RFC PATCH v1] PCI: qcom: Use quirk to override incorrect device class

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Message-ID: <65321fe3-ca29-c454-63ae-98a46c2e5158@mm-sol.com>
Date:   Tue, 12 Mar 2019 14:42:46 +0200
From:   Stanimir Varbanov <svarbanov@...sol.com>
To:     Marc Gonzalez <marc.w.gonzalez@...e.fr>,
        Bjorn Helgaas <bhelgaas@...gle.com>
Cc:     Andy Gross <andy.gross@...aro.org>,
        David Brown <david.brown@...aro.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        PCI <linux-pci@...r.kernel.org>,
        MSM <linux-arm-msm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Jeffrey Hugo <jhugo@...eaurora.org>
Subject: Re: [RFC PATCH v1] PCI: qcom: Use quirk to override incorrect device
 class

Hi Marc,

Thanks for the patch!

On 3/11/19 4:56 PM, Marc Gonzalez wrote:
> Some chips report an incorrect device class. Override the incorrect
> value using a quirk, instead of code in the read function.
> 
> Signed-off-by: Marc Gonzalez <marc.w.gonzalez@...e.fr>
> ---
> FWIW, this quirk is no longer required on recent chips:
> msm8996 (tested by Stanimir), msm8998 (tested by me), sdm845 (untested) are unaffected
> apq/ipq8064 is affected => what is the device ID for these chips?
> others?
> 
> Stanimir added: "this will become a real problem (now we use the driver as RC)
> when someone decide to use it as an endpoint"
> ---
>  drivers/pci/controller/dwc/pcie-qcom.c | 14 ++++++--------
>  1 file changed, 6 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
> index 3de5510fd3d5..94da2c9c2ad5 100644
> --- a/drivers/pci/controller/dwc/pcie-qcom.c
> +++ b/drivers/pci/controller/dwc/pcie-qcom.c
> @@ -1136,17 +1136,15 @@ static int qcom_pcie_rd_own_conf(struct pcie_port *pp, int where, int size,
>  {
>  	struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
>  
> -	/* the device class is not reported correctly from the register */
> -	if (where == PCI_CLASS_REVISION && size == 4) {
> -		*val = readl(pci->dbi_base + PCI_CLASS_REVISION);
> -		*val &= 0xff;	/* keep revision id */
> -		*val |= PCI_CLASS_BRIDGE_PCI << 16;
> -		return PCIBIOS_SUCCESSFUL;
> -	}
> -

once you dropped the above snippet this function becomes absolutely
useless so please delete it at all and also from qcom_pcie_dw_ops.

>  	return dw_pcie_read(pci->dbi_base + where, size, val);
>  }
>  
> +static void qcom_fixup_class(struct pci_dev *dev)
> +{
> +	dev->class = PCI_CLASS_BRIDGE_PCI << 8;
> +}
> +DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_QCOM, PCI_ANY_ID, qcom_fixup_class);

I wonder, in case that dw_pcie_setup_rc() already has a write to
PCI_CLASS_DEVICE configuration register to set it as a bridge do we
still need to do the above fixup?

-- 
regards,
Stan