Re: [PATCH v1 0/5] PolarFire SoC Icicle Reference Design PCIe ?support?/fixes

[Conor Dooley <conor@kernel.org>]

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On Wed, Jul 03, 2024 at 01:09:43PM -0700, Palmer Dabbelt wrote:
> On Mon, 10 Jun 2024 04:09:12 PDT (-0700), Conor Dooley wrote:
> > Hey all,
> > 
> > Here's some patches that add an Erratum to enable non-coherent DMA
> > support for PolarFire SoC. By nature of being an FPGA, and due to the
> > PCIe root ports being only 32-bit capable, many bitstreams configure the
> > FPGA fabric such that peripherals in the fabric become non-coherent. The
> > PCIe root ports on PolarFire SoC are connected to the core-complex via
> > the fabric, and therefore can be (and regularly are) made DMA
> > non-coherent. The Icicle Kit Reference Design has been configuring the
> > PCIe root port in this manner since late 2022 and in a way unsupported
> > by mainline since earlier that year. Adding this non-coherent DMA
> > support makes PCIe functional on those FPGA designs. Daire did almost all
> > the work to figure out how to support these kinds of designs, and this
> > series depends on his patches to introduce the required dma-ranges
> > handling for the root port driver:
> > https://lore.kernel.org/linux-pci/20240531085333.2501399-1-daire.mcnamara@microchip.com/
> > 
> > The final patch depends on:
> > https://lore.kernel.org/linux-pci/20240527-slather-backfire-db4605ae7cd7@wendy/
> > 
> > I'm not sure if an Erratum is really the right way to go about doing
> > this, but I didn't want to make ARCH_MICROCHIP depend on NONPORTABLE.
> > An alternative would be to add a menu under drivers/soc like Renesas
> > does and allow it to be toggled as an option there instead.
> 
> Acked-by: Palmer Dabbelt <palmer@rivosinc.com>
> 
> if you want to take this via some other tree.

Yeah, I was expecting to take it myself but hadn't gone fishing for an
ack because the PCI parts haven't landed yet & the copy in my k.org tree
had a KISMET issue reported against it.

> I don't see any issue calling it an erratum, if it lets us keep building
> generic kernels for these systems that seems like a good enough agrument to
> me.

Cool :)

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