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

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Date:   Fri, 16 Dec 2022 12:34:23 +0300
From:   Serge Semin <fancer.lancer@...il.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Robin Murphy <robin.murphy@....com>,
        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>,
        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

On Thu, Dec 15, 2022 at 11:39:41PM -0800, Christoph Hellwig wrote:
> On Fri, Dec 16, 2022 at 02:52:18AM +0300, Serge Semin wrote:
> > Got it. Thanks for clarification. I'll resubmit the series with only
> > the streaming DMA mask restoration.
> 
> Note that even for that we need to make sure there are no outstanding
> mappings when you change the mask.
> 

What about instead of save/restore pattern I'll just change the
dma_set_mask_and_coherent() method with the dma_set_coherent_mask()
function call? It seems cleaner. Like this:

< --- a/drivers/pci/controller/dwc/pcie-designware-host.c
< +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
< @@ -366,10 +366,10 @@ static int dw_pcie_msi_host_init(struct dw_pcie_rp *pp)
<  						    dw_chained_msi_isr, pp);
<  	}
<  
< -	ret = dma_set_mask_and_coherent(dev, DMA_BIT_MASK(32));
< +	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);

Thus the platform-specific streaming DMA mask would be preserved.
Since it's PCIe then having the streaming DMA-mask less than 32-bits
wide is very much improbable. Moreover DW PCIe AXI-interface can be
synthesize only with one out of two address bus widths: 32 and 64.

-Serge(y)