linux-kernel - Re: [PATCH] PCI: dwc: Set 32-bit DMA mask for MSI target address allocation

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Message-ID: <2fa71e3d-3edc-2667-e4f0-1db62b25f7bc@nvidia.com>
Date:   Thu, 3 Dec 2020 10:32:36 +0530
From:   Vidya Sagar <vidyas@...dia.com>
To:     <jingoohan1@...il.com>, <gustavo.pimentel@...opsys.com>,
        <lorenzo.pieralisi@....com>, <bhelgaas@...gle.com>,
        <robh@...nel.org>
CC:     <linux-pci@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <kthota@...dia.com>, <mmaddireddy@...dia.com>,
        <sagar.tv@...il.com>, <treding@...dia.com>, <jonathanh@...dia.com>
Subject: Re: [PATCH] PCI: dwc: Set 32-bit DMA mask for MSI target address
 allocation

Hi,
Could you please review this patch in the context of the following patch?
http://patchwork.ozlabs.org/project/linux-pci/patch/20201124105035.24573-1-vidyas@nvidia.com/

Thanks,
Vidya Sagar

On 11/17/2020 10:23 PM, Vidya Sagar wrote:
> Set DMA mask to 32-bit while allocating the MSI target address so that
> the address is usable for both 32-bit and 64-bit MSI capable devices.
> Throw a warning if it fails to set the mask to 32-bit to alert that
> devices that are only 32-bit MSI capable may not work properly.
> 
> Signed-off-by: Vidya Sagar <vidyas@...dia.com>
> ---
> Given the other patch that I've pushed to the MSI sub-system
> http://patchwork.ozlabs.org/project/linux-pci/patch/20201117145728.4516-1-vidyas@nvidia.com/
> which is going to catch any mismatch between MSI capability (32-bit) of the
> device and system's inability to allocate the required MSI target address,
> I'm not sure how much sense is this patch going to be make. But, I can
> certainly say that if the memory allocation mechanism gives the addresses
> from 64-bit pool by default, this patch at least makes sure that MSI target
> address is allocated from 32-bit pool.
> 
>   drivers/pci/controller/dwc/pcie-designware-host.c | 8 ++++++++
>   1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> index 44c2a6572199..e6a230eddf66 100644
> --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> @@ -388,6 +388,14 @@ int dw_pcie_host_init(struct pcie_port *pp)
>   							    dw_chained_msi_isr,
>   							    pp);
>   
> +			ret = dma_set_mask(pci->dev, DMA_BIT_MASK(32));
> +			if (!ret) {
> +				dev_warn(pci->dev,
> +					 "Failed to set DMA mask to 32-bit. "
> +					 "Devices with only 32-bit MSI support"
> +					 " may not work properly\n");
> +			}
> +
>   			pp->msi_data = dma_map_single_attrs(pci->dev, &pp->msi_msg,
>   						      sizeof(pp->msi_msg),
>   						      DMA_FROM_DEVICE,
>