linux-kernel - Re: [PATCH v3 10/11] PCI: rockchip: Don't advertise MSI-X in PCIe capabilities

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Message-ID: <c14a2e98-1ca0-35c5-ae05-b44c1baafa7f@fastmail.com>
Date:   Wed, 5 Apr 2023 20:50:37 +0900
From:   Damien Le Moal <dlemoal@...tmail.com>
To:     Rick Wertenbroek <rick.wertenbroek@...il.com>,
        alberto.dassatti@...g-vd.ch
Cc:     damien.lemoal@...nsource.wdc.com, xxm@...k-chips.com,
        Shawn Lin <shawn.lin@...k-chips.com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Rob Herring <robh@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Heiko Stuebner <heiko@...ech.de>,
        Johan Jonker <jbx6244@...il.com>,
        Brian Norris <briannorris@...omium.org>,
        Caleb Connolly <kc@...tmarketos.org>,
        Corentin Labbe <clabbe@...libre.com>,
        Arnaud Ferraris <arnaud.ferraris@...labora.com>,
        Lin Huang <hl@...k-chips.com>,
        Judy Hsiao <judyhsiao@...omium.org>,
        Hugh Cole-Baker <sigmaris@...il.com>,
        linux-pci@...r.kernel.org, linux-rockchip@...ts.infradead.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 10/11] PCI: rockchip: Don't advertise MSI-X in PCIe
 capabilities

On 4/4/23 17:24, Rick Wertenbroek wrote:
> The RK3399 PCIe endpoint controller cannot generate MSI-X IRQs.
> This is documented in the RK3399 technical reference manual (TRM)
> section 17.5.9 "Interrupt Support".
> 
> MSI-X capability should therefore not be advertised. Remove the
> MSI-X capability by editing the capability linked-list. The
> previous entry is the MSI capability, therefore get the next
> entry from the MSI-X capability entry and set it as next entry
> for the MSI capability. This in effect removes MSI-X from the list.
> 
> Linked list before : MSI cap -> MSI-X cap -> PCIe Device cap -> ...
> Linked list now : MSI cap -> PCIe Device cap -> ...
> 
> Signed-off-by: Rick Wertenbroek <rick.wertenbroek@...il.com>
> ---
>  drivers/pci/controller/pcie-rockchip-ep.c | 15 +++++++++++++++
>  drivers/pci/controller/pcie-rockchip.h    |  5 +++++
>  2 files changed, 20 insertions(+)
> 
> diff --git a/drivers/pci/controller/pcie-rockchip-ep.c b/drivers/pci/controller/pcie-rockchip-ep.c
> index 924b95bd736c..20c768287870 100644
> --- a/drivers/pci/controller/pcie-rockchip-ep.c
> +++ b/drivers/pci/controller/pcie-rockchip-ep.c
> @@ -510,6 +510,7 @@ static int rockchip_pcie_ep_probe(struct platform_device *pdev)
>  	size_t max_regions;
>  	struct pci_epc_mem_window *windows = NULL;
>  	int err, i;
> +	u32 cfg_msi, cfg_msix_cp;
>  
>  	ep = devm_kzalloc(dev, sizeof(*ep), GFP_KERNEL);
>  	if (!ep)
> @@ -584,6 +585,20 @@ static int rockchip_pcie_ep_probe(struct platform_device *pdev)
>  
>  	ep->irq_pci_addr = ROCKCHIP_PCIE_EP_DUMMY_IRQ_ADDR;
>  

Nit: Adding a comment here about what this is doing and why would be nice. E.g.
something like:

	/*
	 * MSI-X is not supported but the controller still advertises by default
	 * the MSI-X capability, which can lead to the RC-side attempting to use
	 * MSI-X. Avoid this by skipping the MSI-X capability entry in the
	 * chain of PCIe capabilities: get the next pointer from the
	 * MSI-X entry and set that in the MSI capability entry. This way
	 * the MSI-X entry is skipped (left out of the linked-list).
	 */

> +	cfg_msi = rockchip_pcie_read(rockchip, PCIE_EP_CONFIG_BASE +
> +				     ROCKCHIP_PCIE_EP_MSI_CTRL_REG);
> +
> +	cfg_msi &= ~ROCKCHIP_PCIE_EP_MSI_CP1_MASK;
> +
> +	cfg_msix_cp = rockchip_pcie_read(rockchip, PCIE_EP_CONFIG_BASE +
> +					 ROCKCHIP_PCIE_EP_MSIX_CAP_REG) &
> +					 ROCKCHIP_PCIE_EP_MSIX_CAP_CP_MASK;
> +
> +	cfg_msi |= cfg_msix_cp;
> +
> +	rockchip_pcie_write(rockchip, cfg_msi,
> +			    PCIE_EP_CONFIG_BASE + ROCKCHIP_PCIE_EP_MSI_CTRL_REG);
> +
>  	rockchip_pcie_write(rockchip, PCIE_CLIENT_CONF_ENABLE, PCIE_CLIENT_CONFIG);
>  
>  	return 0;
> diff --git a/drivers/pci/controller/pcie-rockchip.h b/drivers/pci/controller/pcie-rockchip.h
> index 1558eae298ae..a21070ea7166 100644
> --- a/drivers/pci/controller/pcie-rockchip.h
> +++ b/drivers/pci/controller/pcie-rockchip.h
> @@ -226,6 +226,8 @@
>  #define ROCKCHIP_PCIE_EP_CMD_STATUS			0x4
>  #define   ROCKCHIP_PCIE_EP_CMD_STATUS_IS		BIT(19)
>  #define ROCKCHIP_PCIE_EP_MSI_CTRL_REG			0x90
> +#define   ROCKCHIP_PCIE_EP_MSI_CP1_OFFSET		8
> +#define   ROCKCHIP_PCIE_EP_MSI_CP1_MASK			GENMASK(15, 8)
>  #define   ROCKCHIP_PCIE_EP_MSI_FLAGS_OFFSET		16
>  #define   ROCKCHIP_PCIE_EP_MSI_CTRL_MMC_OFFSET		17
>  #define   ROCKCHIP_PCIE_EP_MSI_CTRL_MMC_MASK		GENMASK(19, 17)
> @@ -233,6 +235,9 @@
>  #define   ROCKCHIP_PCIE_EP_MSI_CTRL_MME_MASK		GENMASK(22, 20)
>  #define   ROCKCHIP_PCIE_EP_MSI_CTRL_ME				BIT(16)
>  #define   ROCKCHIP_PCIE_EP_MSI_CTRL_MASK_MSI_CAP	BIT(24)
> +#define ROCKCHIP_PCIE_EP_MSIX_CAP_REG			0xb0
> +#define   ROCKCHIP_PCIE_EP_MSIX_CAP_CP_OFFSET		8
> +#define   ROCKCHIP_PCIE_EP_MSIX_CAP_CP_MASK		GENMASK(15, 8)
>  #define ROCKCHIP_PCIE_EP_DUMMY_IRQ_ADDR				0x1
>  #define ROCKCHIP_PCIE_EP_PCI_LEGACY_IRQ_ADDR		0x3
>  #define ROCKCHIP_PCIE_EP_FUNC_BASE(fn) \