Re: [PATCH v2 02/23] PCI: aardvark: Fix reading MSI interrupt number

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

On Mon, Jan 10, 2022 at 02:49:57AM +0100, Marek Behún wrote:
> From: Pali Rohár <pali@kernel.org>
> 
> In advk_pcie_handle_msi() the authors expect that when bit i in the W1C
> register PCIE_MSI_STATUS_REG is cleared, the PCIE_MSI_PAYLOAD_REG is
> updated to contain the MSI number corresponding to index i.
> 
> Experiments show that this is not so, and instead PCIE_MSI_PAYLOAD_REG
> always contains the number of the last received MSI, overall.
> 
> Do not read PCIE_MSI_PAYLOAD_REG register for determining MSI interrupt
> number. Since Aardvark already forbids more than 32 interrupts and uses
> own allocated hwirq numbers, the msi_idx already corresponds to the
> received MSI number.
> 
> Fixes: 8c39d710363c ("PCI: aardvark: Add Aardvark PCI host controller driver")
> Signed-off-by: Pali Rohár <pali@kernel.org>
> Signed-off-by: Marek Behún <kabel@kernel.org>
> ---
>  drivers/pci/controller/pci-aardvark.c | 9 ++-------
>  1 file changed, 2 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c
> index 62baddd2ca95..fd95ad64c887 100644
> --- a/drivers/pci/controller/pci-aardvark.c
> +++ b/drivers/pci/controller/pci-aardvark.c
> @@ -1393,7 +1393,6 @@ static void advk_pcie_remove_irq_domain(struct advk_pcie *pcie)
>  static void advk_pcie_handle_msi(struct advk_pcie *pcie)
>  {
>  	u32 msi_val, msi_mask, msi_status, msi_idx;
> -	u16 msi_data;
>  
>  	msi_mask = advk_readl(pcie, PCIE_MSI_MASK_REG);
>  	msi_val = advk_readl(pcie, PCIE_MSI_STATUS_REG);
> @@ -1403,13 +1402,9 @@ static void advk_pcie_handle_msi(struct advk_pcie *pcie)
>  		if (!(BIT(msi_idx) & msi_status))
>  			continue;
>  
> -		/*
> -		 * msi_idx contains bits [4:0] of the msi_data and msi_data
> -		 * contains 16bit MSI interrupt number
> -		 */
>  		advk_writel(pcie, BIT(msi_idx), PCIE_MSI_STATUS_REG);
> -		msi_data = advk_readl(pcie, PCIE_MSI_PAYLOAD_REG) & PCIE_MSI_DATA_MASK;

Ok, it took me a while to understand how aardvark handles MSIs.

IIUC, msi_data contains the payload of the latest MSI write received.

First off, I believe that using a Linux IRQ number for MSI data
(payload)(I guess you rely on its truncated bits [4:0] to trigger the
related MSI IRQs, which I believe is questionable - if not broken) is
not a good idea.

Is my understanding correct ?

This patch and the following one are fixing this. Given that this is IRQ
domain code if Marc can cast a look into it that would help me, to make
sure I have not missed anything.

Certainly replacing the MSI payload to the HW irq number makes sense to
me (and this patch makes sense too, I think mainline code may miss some
MSI IRQs if I understand this patch correctly).

Lorenzo

> -		generic_handle_irq(msi_data);
> +		if (generic_handle_domain_irq(pcie->msi_inner_domain, msi_idx) == -EINVAL)
> +			dev_err_ratelimited(&pcie->pdev->dev, "unexpected MSI 0x%02x\n", msi_idx);
>  	}
>  
>  	advk_writel(pcie, PCIE_ISR0_MSI_INT_PENDING,
> -- 
> 2.34.1
>