Re: [PATCH 12/14] PCI: aardvark: Set PCI Bridge Class Code to PCI Bridge

[Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>]

On Tue, Oct 12, 2021 at 06:41:43PM +0200, Marek Behún wrote:
> From: Pali Rohár <pali@kernel.org>
> 
> Aardvark controller has something like config space of a Root Port
> available at offset 0x0 of internal registers - these registers are used
> for implementation of the emulated bridge.
> 
> The default value of Class Code of this bridge corresponds to a RAID Mass
> storage controller, though. (This is probably intended for when the
> controller is used as Endpoint.)
> 
> Change the Class Code to correspond to a PCI Bridge.
> 
> Add comment explaining this change.
> 
> Fixes: 8a3ebd8de328 ("PCI: aardvark: Implement emulated root PCI bridge config space")
> Signed-off-by: Pali Rohár <pali@kernel.org>
> Reviewed-by: Marek Behún <kabel@kernel.org>
> Signed-off-by: Marek Behún <kabel@kernel.org>
> Cc: stable@vger.kernel.org
> ---
>  drivers/pci/controller/pci-aardvark.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c
> index 289cd45ed1ec..801657e7da93 100644
> --- a/drivers/pci/controller/pci-aardvark.c
> +++ b/drivers/pci/controller/pci-aardvark.c
> @@ -513,6 +513,26 @@ static void advk_pcie_setup_hw(struct advk_pcie *pcie)
>  	reg = (PCI_VENDOR_ID_MARVELL << 16) | PCI_VENDOR_ID_MARVELL;
>  	advk_writel(pcie, reg, VENDOR_ID_REG);
>  
> +	/*
> +	 * Change Class Code of PCI Bridge device to PCI Bridge (0x600400),
> +	 * because the default value is Mass storage controller (0x010400).
> +	 *
> +	 * Note that this Aardvark PCI Bridge does not have compliant Type 1
> +	 * Configuration Space and it even cannot be accessed via Aardvark's
> +	 * PCI config space access method. Something like config space is
> +	 * available in internal Aardvark registers starting at offset 0x0
> +	 * and is reported as Type 0. In range 0x10 - 0x34 it has totally
> +	 * different registers.

Is the RP enumerated as a PCI device with type 0 header ?

> +	 *
> +	 * Therefore driver uses emulation of PCI Bridge which emulates
> +	 * access to configuration space via internal Aardvark registers or
> +	 * emulated configuration buffer.
> +	 */
> +	reg = advk_readl(pcie, PCIE_CORE_DEV_REV_REG);
> +	reg &= ~0xffffff00;
> +	reg |= (PCI_CLASS_BRIDGE_PCI << 8) << 8;
> +	advk_writel(pcie, reg, PCIE_CORE_DEV_REV_REG);

I remember Bjorn commenting on something similar in the past - he may
have some comments on whether this change is the right thing to do.

Lorenzo

>  	/* Disable Root Bridge I/O space, memory space and bus mastering */
>  	reg = advk_readl(pcie, PCIE_CORE_CMD_STATUS_REG);
>  	reg &= ~(PCI_COMMAND_IO | PCI_COMMAND_MEMORY | PCI_COMMAND_MASTER);
> -- 
> 2.32.0
>