linux-kernel - Re: [PATCH] usb: gadget: aspeed: set port

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Date:   Fri, 26 Mar 2021 13:05:26 +0100
From:   Christoph Hellwig <hch@....de>
To:     Robin Murphy <robin.murphy@....com>
Cc:     rentao.bupt@...il.com, Felipe Balbi <balbi@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Joel Stanley <joel@....id.au>,
        Andrew Jeffery <andrew@...id.au>,
        kernel test robot <lkp@...el.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Sasha Levin <sashal@...nel.org>,
        Ryan Chen <ryan_chen@...eedtech.com>,
        Thomas Tai <thomas.tai@...cle.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Christoph Hellwig <hch@....de>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        linux-usb@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-aspeed@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        openbmc@...ts.ozlabs.org, Tao Ren <taoren@...com>
Subject: Re: [PATCH] usb: gadget: aspeed: set port_dev dma mask

On Fri, Mar 26, 2021 at 12:03:03PM +0000, Robin Murphy wrote:
> This might happen to work out, but is far from correct. Just wait until you 
> try it on a platform where the USB controller is behind an IOMMU...
>
> It looks like something is more fundamentally wrong here - the device 
> passed to DMA API calls must be the actual hardware device performing the 
> DMA, which in USB-land I believe means the controller's sysdev.

The shiny new usb_intf_get_dma_device API provides the device to use.