linux-kernel - Re: [PATCH v7 23/25] PCI: dwc: Restore DMA-mask after MSI-data allocation

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Date:   Thu, 15 Dec 2022 03:03:23 +0300
From:   Serge Semin <fancer.lancer@...il.com>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Serge Semin <Sergey.Semin@...kalelectronics.ru>,
        Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
        Vinod Koul <vkoul@...nel.org>, Rob Herring <robh@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Cai Huoqing <cai.huoqing@...ux.dev>,
        Robin Murphy <robin.murphy@....com>,
        Jingoo Han <jingoohan1@...il.com>, Frank Li <Frank.Li@....com>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Pavel Parkhomenko <Pavel.Parkhomenko@...kalelectronics.ru>,
        caihuoqing <caihuoqing@...du.com>,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        linux-pci@...r.kernel.org, dmaengine@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 23/25] PCI: dwc: Restore DMA-mask after MSI-data
 allocation

Hi Robin

On Thu, Dec 15, 2022 at 02:53:03AM +0300, Serge Semin wrote:
> DW PCIe Root Ports and End-points can be equipped with the DW eDMA engine.
> In that case it is critical to have the platform device pre-initialized
> with a valid DMA-mask so the drivers using the eDMA-engine would be able
> to allocate the DMA-able buffers. The MSI-capable data requires to be
> allocated from the lowest 4GB region. Since that procedure implies the
> DMA-mask change we need to restore the mask set by the low-level drivers
> after the MSI-data allocation is done.

I dropped the patch
[PATCH v6 22/24] dmaengine: dw-edma: Bypass dma-ranges mapping for the local setup
Link: https://lore.kernel.org/linux-pci/20221107210438.1515-23-Sergey.Semin@baikalelectronics.ru/
from the series. It has turned to be useless since your commit
f1ad5338a4d5 ("of: Fix "dma-ranges" handling for bus controllers").
Instead I added the patches
[PATCH v7 23/25] PCI: dwc: Restore DMA-mask after MSI-data allocation
and
[PATCH v7 24/25] PCI: bt1: Set 64-bit DMA-mask
to this patchset in order to properly handle the DMA-mask.

Could you please give your opinion on these patches?

-Serge(y)

> 
> Signed-off-by: Serge Semin <Sergey.Semin@...kalelectronics.ru>
> 
> ---
> 
> Changelog v7:
> - This is a new patch added on v7 stage of the series. (@Robin)
> ---
>  drivers/pci/controller/dwc/pcie-designware-host.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> index 5762bd306261..1a3dae1f6aa2 100644
> --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> @@ -326,7 +326,7 @@ static int dw_pcie_msi_host_init(struct dw_pcie_rp *pp)
>  	struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
>  	struct device *dev = pci->dev;
>  	struct platform_device *pdev = to_platform_device(dev);
> -	u64 *msi_vaddr;
> +	u64 *msi_vaddr, dma_mask;
>  	int ret;
>  	u32 ctrl, num_ctrls;
>  
> @@ -366,6 +366,13 @@ static int dw_pcie_msi_host_init(struct dw_pcie_rp *pp)
>  						    dw_chained_msi_isr, pp);
>  	}
>  
> +	/*
> +	 * Save and then restore the DMA-mask pre-set by the low-level drivers
> +	 * after allocating the MSI-capable region. The mask might be useful for
> +	 * the controllers with the embedded eDMA engine.
> +	 */
> +	dma_mask = dma_get_mask(dev);
> +
>  	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");
> @@ -378,6 +385,10 @@ static int dw_pcie_msi_host_init(struct dw_pcie_rp *pp)
>  		return -ENOMEM;
>  	}
>  
> +	ret = dma_set_mask_and_coherent(dev, dma_mask);
> +	if (ret)
> +		dev_warn(dev, "Failed to re-store DMA-mask\n");
> +
>  	return 0;
>  }
>  
> -- 
> 2.38.1
> 
>