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

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Date:   Sat, 27 Mar 2021 15:17:59 -0700
From:   Tao Ren <rentao.bupt@...il.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Robin Murphy <robin.murphy@....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>,
        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 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?


Cheers,

Tao