linux-kernel - Re: [PATCH v5 20/20] PCI: dwc: Add Baikal-T1 PCIe controller support

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Message-ID: <20220912002522.arx4vypiv363qcni@mobilestation>
Date:   Mon, 12 Sep 2022 03:25:22 +0300
From:   Serge Semin <fancer.lancer@...il.com>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Serge Semin <Sergey.Semin@...kalelectronics.ru>,
        Rob Herring <robh+dt@...nel.org>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Jingoo Han <jingoohan1@...il.com>,
        Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Pavel Parkhomenko <Pavel.Parkhomenko@...kalelectronics.ru>,
        Frank Li <Frank.Li@....com>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        linux-pci@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, willmcvicker@...gle.com
Subject: Re: [PATCH v5 20/20] PCI: dwc: Add Baikal-T1 PCIe controller support

On Wed, Aug 31, 2022 at 09:54:14AM +0100, Robin Murphy wrote:
> On 2022-08-31 09:36, Robin Murphy wrote:
> > On 2022-08-29 16:28, Lorenzo Pieralisi wrote:
> > [...]
> > > > +static int bt1_pcie_add_port(struct bt1_pcie *btpci)
> > > > +{
> > > > +    struct device *dev = &btpci->pdev->dev;
> > > > +    int ret;
> > > > +
> > > > +    /*
> > > > +     * DW PCIe Root Port controller is equipped with eDMA capable of
> > > > +     * working with the 64-bit memory addresses.
> > > > +     */
> > > > +    ret = dma_set_mask_and_coherent(dev, DMA_BIT_MASK(64));
> > > > +    if (ret)
> > > > +        return ret;
> > > 
> > > Is this the right place to set the DMA mask for the host controller
> > > embedded DMA controller (actually, the dev pointer is the _host_
> > > controller device) ?
> > > 
> > > How this is going to play when combined with:
> > > 
> > > https://lore.kernel.org/linux-pci/1e63a581-14ae-b4b5-a5bf-ca8f09c33af6@arm.com
> > > 
> > > It is getting a bit confusing. I believe the code in the link
> > > above sets the mask so that through the DMA API we are capable
> > > of getting an MSI doorbell virtual address whose physical address
> > > can be addressed by the endpoint; this through the DMA API.
> > > 
> > > This patch is setting the DMA mask for a different reason, namely
> > > setting the host controller embedded DMA controller addressing
> > > capabilities.
> > > 
> > > AFAICS - both approaches set the mask for the same device - now
> > > the question is about which one is legitimate and how to handle
> > > the other.
> > 
> > Assuming the dw-edma-pcie driver is the relevant one, that already sets
> > its own masks on its own device, so I also don't see why this is here.
> 

> Ah, I just found the patch at [1], which further implies that this is indeed
> completely bogus.

Really? Elaborate please. What you said in the comment to that patch
has nothing to do with the change you comment here.

-Sergey

> 
> Robin.
> 
> [1] https://lore.kernel.org/dmaengine/20220822185332.26149-23-Sergey.Semin@baikalelectronics.ru/