linux-kernel - Re: [PATCH] of: Devices with pci_epf_bus

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Date:   Mon, 23 Oct 2017 08:31:13 +0200
From:   Christoph Hellwig <hch@....de>
To:     Kishon Vijay Abraham I <kishon@...com>
Cc:     Robin Murphy <robin.murphy@....com>,
        Christoph Hellwig <hch@....de>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        linux-omap@...r.kernel.org, linux-pci@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        nsekhar@...com
Subject: Re: [PATCH] of: Devices with pci_epf_bus_type require DMA
        configuration

On Mon, Oct 23, 2017 at 11:13:23AM +0530, Kishon Vijay Abraham I wrote:
> EPF devices use EPC devices which in turn use the actual platform device for
> configuring the hardware. IMO the devices in one layer shouldn't have to
> explicitly use devices in another layer other than using clearly defined API's.
> Here platform_device is the bottom later, above which is epc_device and on top
> is epf_device.
> 
> The idea is just by doing the initial setup in the framework, the epf driver be
> able to use APIs like dma_alloc_coherent using it's own *device* rather than
> the EPC's "device".

That's a little strange - normally we only call dma_map* routines on
the actual physical bus devices.