[PATCH v4 4/8] PCI: brcmstb: Add dma-range mapping for inbound traffic
jim2101024 at gmail.com
Mon Feb 12 05:39:43 PST 2018
On Fri, Jan 26, 2018 at 12:46 PM, Jim Quinlan <jim2101024 at gmail.com> wrote:
> On Fri, Jan 26, 2018 at 2:53 AM, Christoph Hellwig <hch at lst.de> wrote:
>> On Wed, Jan 24, 2018 at 12:04:58PM -0800, Florian Fainelli wrote:
>>> This looks nicer than the current shape, but this still requires to
>>> register a PCI fixup to override phys_to_dma() and dma_to_phys(), and it
>>> would appear that you have dodged my question about how this is supposed
>>> to fit with an entirely modular PCIe root complex driver? Are you
>>> suggesting that we split the module into a built-in part and a modular part?
>> I don't think entirely modular PCI root bridges should be a focal point
>> for the design. If we happen to support them by other design choices:
>> fine, but they should not be a priority.
> I disagree. If there is one common thing our customers request it is
> the ability to remove (or control the insmod of after boot) the pcie
> RC driver. I didn't add this in as a "nice-to-have".
>> That being said if we have core dma mapping or PCIe code that has
>> a list of offsets and the root complex only populates them it should
>> work just fine.
> I'm looking at arch/arm/include/asm/dma-mapping.h. In addition to
> overriding dma_to_phsy() and phys_to_dma(), it looks like I may have
> to define __arch_pfn_to_dma(), __arch_dma_to_pfn(),
> __arch_dma_to_virt(), __arch_virt_to_dma(). Do you agree or is this
> not necessary? If it is, this seems more intrusive than our
> pcie-brcmstb-dma.c solution which doesn't require tentacles into
> major include files and Kconfigs.
> Another issue is that our function wrappers -- depending upon whether
> we are dealing with a pci device or not -- will have to possibly call
> the actual ARM and ARM64 definitions of these functions, which have
> been of course #ifdef'd out. This means that our code must contain
> identical copies of these functions' code and that the code must
> somehow be kept in sync. Do you see a solution to this?
Could you please respond to my comments? Even a negative response is
better than none. The problem with doing what you suggested is with
ARM -- ARM64 and MIPS relatively uncomplicated . With ARM, I have to
define the aforementioned functions -- the only way of doing this is
to define arch/arm/mach-bcm/include/mach/memory.h, and for that to be
picked up we no longer can have CONFIG_ARCH_MULTIPLATFORM=y, which is
an unacceptable cost to pay for just an unusual PCIe RC controller.
Regarding my current submission -- you are right, SWIOTLB will not
work for EPs that require it. However, we don't care about these
devices, and can just bailout with EPs when the dma_mask is <=
0xffff_ffff or if swiotlb_force == SWIOTLB_FORCE. Note that this
would only affect PCIe DMA. We also have no plan of using MIPS64.
More information about the linux-arm-kernel