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

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Date:   Thu, 24 Oct 2019 10:24:02 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     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>
Cc:     "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 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. ioremap() typically just uses
virtual address space in the VMALLOC region, PCI doesn't need it's own
range. As far as I know the ioremap() implementation in riscv already
does this.

In any case, 16MB for PCI bar space seems woefully inadequate.

Logan


> Signed-off-by: Yash Shah <yash.shah@...ive.com>
> ---
>  arch/riscv/include/asm/io.h      | 7 +++++++
>  arch/riscv/include/asm/pgtable.h | 7 ++++++-
>  2 files changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/riscv/include/asm/io.h b/arch/riscv/include/asm/io.h
> index fc1189a..3ba4d93 100644
> --- a/arch/riscv/include/asm/io.h
> +++ b/arch/riscv/include/asm/io.h
> @@ -13,6 +13,7 @@
>  
>  #include <linux/types.h>
>  #include <asm/mmiowb.h>
> +#include <asm/pgtable.h>
>  
>  extern void __iomem *ioremap(phys_addr_t offset, unsigned long size);
>  
> @@ -162,6 +163,12 @@ static inline u64 __raw_readq(const volatile void __iomem *addr)
>  #endif
>  
>  /*
> + *  I/O port access constants.
> + */
> +#define IO_SPACE_LIMIT		(PCI_IO_SIZE - 1)
> +#define PCI_IOBASE		((void __iomem *)PCI_IO_START)
> +
> +/*
>   * Emulation routines for the port-mapped IO space used by some PCI drivers.
>   * These are defined as being "fully synchronous", but also "not guaranteed to
>   * be fully ordered with respect to other memory and I/O operations".  We're
> diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> index 7fc5e4a..d78cc74 100644
> --- a/arch/riscv/include/asm/pgtable.h
> +++ b/arch/riscv/include/asm/pgtable.h
> @@ -7,6 +7,7 @@
>  #define _ASM_RISCV_PGTABLE_H
>  
>  #include <linux/mmzone.h>
> +#include <linux/sizes.h>
>  
>  #include <asm/pgtable-bits.h>
>  
> @@ -88,6 +89,7 @@ extern pgd_t swapper_pg_dir[];
>  #define VMALLOC_SIZE     (KERN_VIRT_SIZE >> 1)
>  #define VMALLOC_END      (PAGE_OFFSET - 1)
>  #define VMALLOC_START    (PAGE_OFFSET - VMALLOC_SIZE)
> +#define PCI_IO_SIZE      SZ_16M
>  
>  /*
>   * Roughly size the vmemmap space to be large enough to fit enough
> @@ -102,7 +104,10 @@ extern pgd_t swapper_pg_dir[];
>  
>  #define vmemmap		((struct page *)VMEMMAP_START)
>  
> -#define FIXADDR_TOP      (VMEMMAP_START)
> +#define PCI_IO_END       VMEMMAP_START
> +#define PCI_IO_START     (PCI_IO_END - PCI_IO_SIZE)
> +#define FIXADDR_TOP      PCI_IO_START
> +
>  #ifdef CONFIG_64BIT
>  #define FIXADDR_SIZE     PMD_SIZE
>  #else
>