linux-kernel - Re: [PATCH v2 1/2] PCI: dwc: drop dependency on ZONE

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Date:   Wed, 10 Aug 2022 15:27:16 -0600
From:   Rob Herring <robh@...nel.org>
To:     Will McVicker <willmcvicker@...gle.com>
Cc:     Jingoo Han <jingoohan1@...il.com>,
        Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>, kernel-team@...roid.com,
        Vidya Sagar <vidyas@...dia.com>,
        kernel test robot <lkp@...el.com>,
        "Isaac J . Manjarres" <isaacmanjarres@...gle.com>,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] PCI: dwc: drop dependency on ZONE_DMA32

On Wed, Aug 10, 2022 at 06:35:34PM +0000, Will McVicker wrote:
> Re-work the msi_msg DMA allocation logic to use dma_alloc_coherent()
> which uses the coherent DMA mask to try and return an allocation within
> the DMA mask limits. This allows kernel configurations that disable
> ZONE_DMA32 to continue supporting a 32-bit DMA mask. Without this patch,
> the PCIe host device will fail to probe when ZONE_DMA32 is disabled.
> 
> Fixes: 35797e672ff0 ("PCI: dwc: Fix MSI msi_msg DMA mapping")
> Reported-by: Isaac J. Manjarres <isaacmanjarres@...gle.com>
> Signed-off-by: Will McVicker <willmcvicker@...gle.com>
> ---
>  .../pci/controller/dwc/pcie-designware-host.c | 23 ++++++++-----------
>  1 file changed, 9 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> index 7746f94a715f..8f2222f51671 100644
> --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> @@ -272,9 +272,9 @@ static void dw_pcie_free_msi(struct dw_pcie_rp *pp)
>  		struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
>  		struct device *dev = pci->dev;
>  
> -		dma_unmap_page(dev, pp->msi_data, PAGE_SIZE, DMA_FROM_DEVICE);
> -		if (pp->msi_page)
> -			__free_page(pp->msi_page);
> +		dma_free_coherent(dev, PAGE_SIZE, pp->msi_page, pp->msi_data);
> +		pp->msi_data = 0;
> +		pp->msi_page = NULL;
>  	}
>  }
>  
> @@ -375,22 +375,17 @@ static int dw_pcie_msi_host_init(struct dw_pcie_rp *pp)
>  						    dw_chained_msi_isr, pp);
>  	}
>  
> -	ret = dma_set_mask(dev, DMA_BIT_MASK(32));
> +	ret = dma_set_mask_and_coherent(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");
>  
> -	pp->msi_page = alloc_page(GFP_DMA32);
> -	pp->msi_data = dma_map_page(dev, pp->msi_page, 0,
> -				    PAGE_SIZE, DMA_FROM_DEVICE);
> -	ret = dma_mapping_error(dev, pp->msi_data);
> -	if (ret) {
> -		dev_err(pci->dev, "Failed to map MSI data\n");
> -		__free_page(pp->msi_page);
> -		pp->msi_page = NULL;
> +	pp->msi_page = dma_alloc_coherent(dev, PAGE_SIZE, &pp->msi_data,
> +					  GFP_KERNEL);

You can use the managed version, dmam_alloc_coherent(), and avoid the 
freeing yourself. Also with that, I think you don't need 'msi_page'?

Also, no need to alloc a whole page. A u32 or u64? should be fine. The 
write never makes it to memory, so doesn't really matter.

> +	if (!pp->msi_page) {
> +		dev_err(dev, "Failed to alloc and map MSI data\n");
>  		pp->msi_data = 0;
>  		dw_pcie_free_msi(pp);
> -
> -		return ret;
> +		return -ENOMEM;
>  	}
>  
>  	return 0;
> -- 
> 2.37.1.559.g78731f0fdb-goog
>