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Date: Mon, 29 Mar 2021 08:17:35 +0200
From: Christoph Hellwig <hch@lst.de>
To: Tao Ren <rentao.bupt@gmail.com>
Subject: Re: [PATCH] usb: gadget: aspeed: set port_dev dma mask
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Cc: Sasha Levin <sashal@kernel.org>, Felipe Balbi <balbi@kernel.org>,
 linux-usb@vger.kernel.org, Ryan Chen <ryan_chen@aspeedtech.com>,
 kernel test robot <lkp@intel.com>, linux-aspeed@lists.ozlabs.org,
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 Andrew Jeffery <andrew@aj.id.au>,
 Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
 Masahiro Yamada <masahiroy@kernel.org>, Thomas Tai <thomas.tai@oracle.com>,
 Tao Ren <taoren@fb.com>, linux-kernel@vger.kernel.org,
 openbmc@lists.ozlabs.org, Robin Murphy <robin.murphy@arm.com>,
 Christoph Hellwig <hch@lst.de>, linux-arm-kernel@lists.infradead.org
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On Sat, Mar 27, 2021 at 03:17:59PM -0700, Tao Ren wrote:
> On Fri, Mar 26, 2021 at 01:05:26PM +0100, Christoph Hellwig wrote:
> > 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.
> 
> Thanks Robin and Christoph for the feedback.
> 
> If I understand correctly, usb_intf_get_dma_device API is mainly for usb
> host drivers? I just found usb_gadget_map_request_by_dev API: does it
> make sense to replace usb_gadget_map_request with
> usb_gadget_map_request_by_dev so we can pass the actual DMA-capable
> hardware device (aspeed-vhub platform device) to the API?

Oh, right you're dealing with a gadget side driver.  Not sure about
the API there, I'll let the relevant maintainers chime in.