linux-kernel - Re: [PATCH] RISC-V: Add PCIe I/O BAR memory mapping

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Date:   Thu, 24 Oct 2019 11:07:12 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Paul Walmsley <paul.walmsley@...ive.com>
Cc:     Yash Shah <yash.shah@...ive.com>,
        "Paul Walmsley ( Sifive)" <paul.walmsley@...ifive.com>,
        "Palmer Dabbelt ( Sifive)" <palmer@...ifive.com>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "sorear2@...il.com" <sorear2@...il.com>,
        "aou@...s.berkeley.edu" <aou@...s.berkeley.edu>,
        "alex@...ti.fr" <alex@...ti.fr>,
        "catalin.marinas@....com" <catalin.marinas@....com>,
        "Anup.Patel@....com" <Anup.Patel@....com>,
        "rppt@...ux.ibm.com" <rppt@...ux.ibm.com>,
        Sachin Ghadi <sachin.ghadi@...ive.com>,
        Greentime Hu <greentime.hu@...ifive.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "will@...nel.org" <will@...nel.org>,
        "allison@...utok.net" <allison@...utok.net>
Subject: Re: [PATCH] RISC-V: Add PCIe I/O BAR memory mapping



On 2019-10-24 10:51 a.m., Paul Walmsley wrote:
> On Thu, 24 Oct 2019, Logan Gunthorpe wrote:
> 
>> On 2019-10-24 3:14 a.m., Yash Shah wrote:
>>> For I/O BARs to work correctly on RISC-V Linux, we need to establish a
>>> reserved memory region for them, so that drivers that wish to use I/O BARs
>>> can issue reads and writes against a memory region that is mapped to the
>>> host PCIe controller's I/O BAR MMIO mapping.
>>
>> I don't think other arches do this. 
> 
> $ git grep 'define PCI_IOBASE' arch/ 
> arch/arm/include/asm/io.h:#define PCI_IOBASE            ((void __iomem *)PCI_IO_VIRT_BASE)
> arch/arm64/include/asm/io.h:#define PCI_IOBASE          ((void __iomem *)PCI_IO_START)
> arch/m68k/include/asm/io_no.h:#define PCI_IOBASE        ((void __iomem *) PCI_IO_PA)
> arch/microblaze/include/asm/io.h:#define PCI_IOBASE     ((void __iomem *)_IO_BASE)
> arch/unicore32/include/asm/io.h:#define PCI_IOBASE      PKUNITY_PCILIO_BASE
> arch/xtensa/include/asm/io.h:#define PCI_IOBASE         ((void __iomem *)XCHAL_KIO_BYPASS_VADDR)
> $
> 
> This is for the old x86-style, non-memory mapped I/O address space the 
> legacy PCI stuff that one would use in{b,w,l}()/out{b,w,l}() for.
> 
> Yash, you might consider updating your patch description to note that this 
> is for "legacy I/O BARs (i.e., non-MMIO BARs)" or something similar.  That 
> might make things clearer.

Ah, right, yes, that would clear things up.

Logan