Re: [PATCH v2] PCI: dwc: Strengthen the MSI address allocation logic

[William McVicker <willmcvicker@google.com>]

Hi Ajay,

Thanks for sending the patch!

On 01/11/2024, Ajay Agarwal wrote:
> There can be platforms that do not use/have 32-bit DMA addresses
> but want to enumerate endpoints which support only 32-bit MSI
> address. The current implementation of 32-bit IOVA allocation can
> fail for such platforms, eventually leading to the probe failure.
> 
> If there is a memory region reserved for the pci->dev, pick up
> the MSI data from this region. This can be used by the platforms
> described above.
> 
> Else, if the memory region is not reserved, try to allocate a
> 32-bit IOVA. Additionally, if this allocation also fails, attempt
> a 64-bit allocation for probe to be successful. If the 64-bit MSI
> address is allocated, then the EPs supporting 32-bit MSI address
> will not work.
> 
> Signed-off-by: Ajay Agarwal <ajayagarwal@google.com>
> ---
> Changelog since v1:
>  - Use reserved memory, if it exists, to setup the MSI data
>  - Fallback to 64-bit IOVA allocation if 32-bit allocation fails
> 
>  .../pci/controller/dwc/pcie-designware-host.c | 50 ++++++++++++++-----
>  drivers/pci/controller/dwc/pcie-designware.h  |  1 +
>  2 files changed, 39 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> index 7991f0e179b2..8c7c77b49ca8 100644
> --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> @@ -331,6 +331,8 @@ static int dw_pcie_msi_host_init(struct dw_pcie_rp *pp)
>  	u64 *msi_vaddr;
>  	int ret;
>  	u32 ctrl, num_ctrls;
> +	struct device_node *np;
> +	struct resource r;
>  
>  	for (ctrl = 0; ctrl < MAX_MSI_CTRLS; ctrl++)
>  		pp->irq_mask[ctrl] = ~0;
> @@ -374,20 +376,44 @@ static int dw_pcie_msi_host_init(struct dw_pcie_rp *pp)
>  	 * order not to miss MSI TLPs from those devices the MSI target
>  	 * address has to be within the lowest 4GB.
>  	 *
> -	 * Note until there is a better alternative found the reservation is
> -	 * done by allocating from the artificially limited DMA-coherent
> -	 * memory.
> +	 * Check if there is memory region reserved for this device. If yes,
> +	 * pick up the msi_data from this region. This will be helpful for
> +	 * platforms that do not use/have 32-bit DMA addresses but want to use
> +	 * endpoints which support only 32-bit MSI address.
> +	 * Else, if the memory region is not reserved, try to allocate a 32-bit
> +	 * IOVA. Additionally, if this allocation also fails, attempt a 64-bit
> +	 * allocation. If the 64-bit MSI address is allocated, then the EPs
> +	 * supporting 32-bit MSI address will not work.
>  	 */
> -	ret = dma_set_coherent_mask(dev, DMA_BIT_MASK(32));
> -	if (ret)
> -		dev_warn(dev, "Failed to set DMA mask to 32-bit. Devices with only 32-bit MSI support may not work properly\n");
> +	np = of_parse_phandle(dev->of_node, "memory-region", 0);
> +	if (np) {
> +		ret = of_address_to_resource(np, 0, &r);
> +		if (ret) {
> +			dev_err(dev, "No memory address assigned to the region\n");
> +			return ret;
> +		}
>  
> -	msi_vaddr = dmam_alloc_coherent(dev, sizeof(u64), &pp->msi_data,
> -					GFP_KERNEL);
> -	if (!msi_vaddr) {
> -		dev_err(dev, "Failed to alloc and map MSI data\n");
> -		dw_pcie_free_msi(pp);
> -		return -ENOMEM;
> +		pp->msi_data = r.start;
> +	} else {
> +		dev_dbg(dev, "No %s specified\n", "memory-region");
> +		ret = dma_set_coherent_mask(dev, DMA_BIT_MASK(32));
> +		if (ret)
> +			dev_warn(dev, "Failed to set DMA mask to 32-bit. Devices with only 32-bit MSI support may not work properly\n");
> +
> +		msi_vaddr = dmam_alloc_coherent(dev, sizeof(u64), &pp->msi_data,
> +						GFP_KERNEL);
> +		if (!msi_vaddr) {
> +			dev_warn(dev, "Failed to alloc 32-bit MSI data. Attempting 64-bit now\n");
> +			dma_set_coherent_mask(dev, DMA_BIT_MASK(64));
> +			msi_vaddr = dmam_alloc_coherent(dev, sizeof(u64), &pp->msi_data,
> +							GFP_KERNEL);
> +		}
> +
> +		if (!msi_vaddr) {
> +			dev_err(dev, "Failed to alloc and map MSI data\n");
> +			dw_pcie_free_msi(pp);
> +			return -ENOMEM;
> +		}

Should we just put this second if-check inside the above fallback?

>  	}
>  
>  	return 0;
> diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
> index 55ff76e3d384..c85cf4d56e98 100644
> --- a/drivers/pci/controller/dwc/pcie-designware.h
> +++ b/drivers/pci/controller/dwc/pcie-designware.h
> @@ -317,6 +317,7 @@ struct dw_pcie_rp {
>  	phys_addr_t		io_bus_addr;
>  	u32			io_size;
>  	int			irq;
> +	u8			coherent_dma_bits;
>  	const struct dw_pcie_host_ops *ops;
>  	int			msi_irq[MAX_MSI_CTRLS];
>  	struct irq_domain	*irq_domain;

Looks like this is a lingering change? Please drop.

Thanks,
Will

> -- 
> 2.43.0.275.g3460e3d667-goog
>