From: Bjorn Helgaas <bhelgaas@google.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Santosh Shilimkar <santosh.shilimkar@ti.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
linux-arm <linux-arm-kernel@lists.infradead.org>,
"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Russell King <linux@arm.linux.org.uk>,
Olof Johansson <olof@lixom.net>,
Grant Likely <grant.likely@linaro.org>,
Rob Herring <robh+dt@kernel.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Linus Walleij <linus.walleij@linaro.org>,
Grygorii Strashko <grygorii.strashko@ti.com>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Chris Metcalf <cmetcalf@tilera.com>
Subject: Re: [PATCH v3 4/7] of: configure the platform device dma parameters
Date: Mon, 5 May 2014 14:45:21 -0600 [thread overview]
Message-ID: <CAErSpo5-FXmVs8BWRYKz9Ln1g1Ls7_uo3oiPd32fUegf3d8hXQ@mail.gmail.com> (raw)
In-Reply-To: <20923376.buVzFR52Qe@wuerfel>
[+cc Ben, Chris]
On Fri, May 2, 2014 at 12:59 PM, Arnd Bergmann <arnd@arndb.de> wrote:
> On Friday 02 May 2014 10:54:59 Bjorn Helgaas wrote:
>> > +static void of_dma_configure(struct device *dev)
>> > +{
>> > + u64 dma_addr, paddr, size;
>> > + int ret;
>> > +
>> > + dev->coherent_dma_mask = DMA_BIT_MASK(32);
>> > + if (!dev->dma_mask)
>> > + dev->dma_mask = &dev->coherent_dma_mask;
>> > +
>> > + /*
>> > + * if dma-coherent property exist, call arch hook to setup
>> > + * dma coherent operations.
>> > + */
>> > + if (of_dma_is_coherent(dev->of_node)) {
>> > + set_arch_dma_coherent_ops(dev);
>> > + dev_dbg(dev, "device is dma coherent\n");
>> > + }
>> > +
>> > + /*
>> > + * if dma-ranges property doesn't exist - just return else
>> > + * setup the dma offset
>> > + */
>> > + ret = of_dma_get_range(dev->of_node, &dma_addr, &paddr, &size);
>> > + if ((ret == -ENODEV) || (ret < 0)) {
>> > + dev_dbg(dev, "no dma range information to setup\n");
>> > + return;
>> > + }
>> > +
>> > + /* DMA ranges found. Calculate and set dma_pfn_offset */
>> > + dev->dma_pfn_offset = PFN_DOWN(paddr - dma_addr);
>> > + dev_dbg(dev, "dma_pfn_offset(%#08lx)\n", dev->dma_pfn_offset);
>>
>> Is this effectively the same as an IOMMU that applies a constant offset
>> to the bus address? Could or should this be done by adding a simple IOMMU
>> driver instead of adding dma_pfn_offset to struct device?
>
> We currently have two dma_map_ops variants on ARM (plus another set for
> coherent/noncoherent differences, but we can ignore that for the sake
> of this discussion): one that handles linear mappings and one that
> handles IOMMUs by calling into the linux/iommu.h APIs.
>
> I guess what you mean by 'a simple IOMMU driver' would be another
> dma_map_ops implementation that is separate from real IOMMUs, right?
I suppose so; it seems like the offset could be managed inside
arm_dma_ops. My idea of an IOMMU is something that maps bus addresses
to physical memory addresses. That's what we're doing here; it's just
that the mapping function is very simple. So why add something new in
struct device for it?
I think powerpc and tile do something similar in dma_direct_map_page()
and tile_pci_dma_map_page() (they store the offset in struct
dev_archdata).
Bjorn
next prev parent reply other threads:[~2014-05-05 20:45 UTC|newest]
Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-04-24 15:30 [PATCH v3 0/7] of: setup dma parameters using dma-ranges and dma-coherent Santosh Shilimkar
2014-04-24 15:30 ` [PATCH v3 1/7] device: introduce per device dma_pfn_offset Santosh Shilimkar
2014-05-02 1:01 ` Rob Herring
2014-04-24 15:30 ` [PATCH v3 2/7] of: introduce of_dma_get_range() helper Santosh Shilimkar
2014-05-02 1:06 ` Rob Herring
2014-04-24 15:30 ` [PATCH v3 3/7] of: introduce of_dma_is_coherent() helper Santosh Shilimkar
2014-05-02 0:56 ` Rob Herring
2014-05-05 21:45 ` Santosh Shilimkar
2014-05-05 22:06 ` Rob Herring
2014-04-24 15:30 ` [PATCH v3 4/7] of: configure the platform device dma parameters Santosh Shilimkar
2014-04-29 14:41 ` Grant Likely
2014-04-30 14:19 ` Santosh Shilimkar
2014-05-01 13:12 ` Grant Likely
2014-05-01 13:16 ` Santosh Shilimkar
2014-05-02 9:58 ` Arnd Bergmann
2014-05-02 13:13 ` Santosh Shilimkar
2014-05-02 15:13 ` Arnd Bergmann
2014-05-27 12:56 ` Grant Likely
2014-05-27 13:30 ` Arnd Bergmann
2014-05-28 8:23 ` Linus Walleij
2014-05-28 13:29 ` Arnd Bergmann
2014-05-28 13:32 ` Linus Walleij
2014-05-28 14:04 ` Santosh Shilimkar
2014-05-29 14:01 ` Linus Walleij
2014-05-29 14:08 ` Santosh Shilimkar
2014-05-29 19:24 ` Arnd Bergmann
2014-05-29 20:04 ` Santosh Shilimkar
2014-05-02 0:49 ` Rob Herring
2014-05-05 21:47 ` Santosh Shilimkar
2014-05-05 22:08 ` Rob Herring
2014-05-06 9:40 ` Arnd Bergmann
2014-05-06 20:44 ` Santosh Shilimkar
2014-05-07 13:24 ` Santosh Shilimkar
2014-05-02 16:54 ` Bjorn Helgaas
2014-05-02 18:59 ` Arnd Bergmann
2014-05-05 20:45 ` Bjorn Helgaas [this message]
2014-05-05 20:55 ` Arnd Bergmann
2014-05-05 22:28 ` Bjorn Helgaas
2014-05-06 3:44 ` Benjamin Herrenschmidt
2014-05-06 9:54 ` Arnd Bergmann
2014-05-06 13:32 ` Santosh Shilimkar
2014-04-24 15:30 ` [PATCH v3 5/7] ARM: dma: Use dma_pfn_offset for dma address translation Santosh Shilimkar
2014-05-02 14:32 ` Rob Herring
2014-05-02 14:58 ` Russell King - ARM Linux
2014-05-02 15:05 ` Santosh Shilimkar
2014-05-05 19:50 ` Russell King - ARM Linux
2014-05-05 21:43 ` Santosh Shilimkar
2014-04-24 15:30 ` [PATCH v3 6/7] ARM: dma: implement set_arch_dma_coherent_ops() Santosh Shilimkar
2014-05-02 0:58 ` Rob Herring
2014-04-24 15:30 ` [PATCH v3 7/7] ARM: dma: use phys_addr_t in __dma_page_[cpu_to_dev/dev_to_cpu] Santosh Shilimkar
2014-04-24 15:45 ` Will Deacon
2014-05-01 13:19 ` [PATCH v3 0/7] of: setup dma parameters using dma-ranges and dma-coherent Santosh Shilimkar
2014-05-01 13:25 ` Russell King - ARM Linux
2014-05-01 14:06 ` Santosh Shilimkar
2014-05-02 14:41 ` Rob Herring
2014-05-02 16:41 ` Santosh Shilimkar
2014-05-14 10:12 ` Grant Likely
2014-06-02 6:37 ` Shawn Guo
2014-06-02 13:24 ` Santosh Shilimkar
2014-06-02 15:06 ` Arnd Bergmann
2014-06-02 15:54 ` Santosh Shilimkar
2014-06-02 19:00 ` Arnd Bergmann
2014-06-02 19:08 ` Santosh Shilimkar
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