From mboxrd@z Thu Jan  1 00:00:00 1970
From: hch@lst.de (Christoph Hellwig)
Date: Mon, 6 Aug 2018 18:34:16 +0200
Subject: [PATCH 2/3] PCI/xilinx: Work-around for hardware DMA limit (32
 bits)
In-Reply-To: <CAMgXwTjcjdiBN9yksL9zuZQyGjckC+F+qwzSm32RjjFSWHFCPQ@mail.gmail.com>
References: <20180804101402.10022-1-hch@lst.de>
 <20180804101402.10022-3-hch@lst.de>
 <CAMgXwTgr572J_HH396tfvT7Zj8Jj0fefKOSmVw2+Gwn8qcPR1g@mail.gmail.com>
 <20180806123527.GB6997@lst.de>
 <CAMgXwTjcjdiBN9yksL9zuZQyGjckC+F+qwzSm32RjjFSWHFCPQ@mail.gmail.com>
Message-ID: <20180806163416.GA18429@lst.de>
To: linux-riscv@lists.infradead.org
List-Id: linux-riscv.lists.infradead.org

On Mon, Aug 06, 2018 at 09:21:40AM -0700, Wesley Terpstra wrote:
> On Mon, Aug 6, 2018 at 5:35 AM, Christoph Hellwig <hch@lst.de> wrote:
> > Note that we already have the mechanism for firmware directed dma limits
> > in place, it is called the dma-ranges DT property.  If we can get the
> > SiFive firmware to set it up properly the RISC-V swiotlb code will
> > just do the right thing.
> 
> Does this mean we only need to set the dma-ranges property inside the
> pci DTS node? No changes to the driver needed?

The code looks at the DT parent of the PCI bridge device.  Take a look
at drivers/pci/pci-driver.c:pci_dma_configure() and
drivers/of/device.c:of_dma_configure() in 4.18-rc (for older kernels
the involved functions are slightly different, but the functionality
is the same).