Re: [PATCH v4] PCI: dwc: Strengthen the MSI address allocation logic

[Manivannan Sadhasivam <mani@kernel.org>]

On Wed, Feb 14, 2024 at 11:04:15AM +0530, 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 the vendor driver has already setup the MSI address using
> some mechanism, use the same. This method can be used by the
> platforms described above to support EPs they wish to. Such
> drivers should set the DW_PCIE_CAP_MSI_DATA_SET flag.
> 
> Else, 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 v3:
>  - Add a new controller cap flag 'DW_PCIE_CAP_MSI_DATA_SET'
>  - Refactor the comments and print statements
> 
> Changelog since v2:
>  - If the vendor driver has setup the msi_data, use the same
> 
> 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  | 18 +++++++++++++++---
>  drivers/pci/controller/dwc/pcie-designware.h   |  1 +
>  2 files changed, 16 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> index d5fc31f8345f..06ee2e5deebc 100644
> --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> @@ -373,11 +373,17 @@ static int dw_pcie_msi_host_init(struct dw_pcie_rp *pp)
>  	 * peripheral PCIe devices may lack 64-bit message support. In
>  	 * order not to miss MSI TLPs from those devices the MSI target
>  	 * address has to be within the lowest 4GB.
> +	 * Permit the platforms to override the MSI target address if they
> +	 * have a free PCIe-bus memory specifically reserved for that. Such
> +	 * platforms should set the 'DW_PCIE_CAP_MSI_DATA_SET' cap flag.
>  	 *
>  	 * Note until there is a better alternative found the reservation is
>  	 * done by allocating from the artificially limited DMA-coherent
>  	 * memory.
>  	 */

Now the above comments are misplaced. Please move the comments related to
setting coherent mask just above the dma_set_coherent_mask() API and keep the
flag related comments here.

> +	if (dw_pcie_cap_is(pci, MSI_DATA_SET))

Who is setting this flag? You should not add code when there are no in-kernel
consumers.

> +		return 0;
> +
>  	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");
> @@ -385,9 +391,15 @@ static int dw_pcie_msi_host_init(struct dw_pcie_rp *pp)
>  	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;
> +		dev_warn(dev, "Failed to configure 32-bit MSI address. Devices with only 32-bit MSI support may not work properly\n");

This is a duplicated error log.

> +		dma_set_coherent_mask(dev, DMA_BIT_MASK(64));

Is there a guarantee that this will never fail?

- Mani

-- 
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