linux-kernel - Re: [PATCH v4 1/8] swiotlb: make io_tlb_default

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Date:   Mon, 17 Jul 2023 08:06:07 +0200
From:   Philippe Mathieu-Daudé <philmd@...aro.org>
To:     Petr Tesarik <petrtesarik@...weicloud.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Juergen Gross <jgross@...e.com>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        Petr Tesarik <petr.tesarik.ext@...wei.com>,
        Jonathan Corbet <corbet@....net>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Hans de Goede <hdegoede@...hat.com>,
        James Seo <james@...iv.tech>,
        James Clark <james.clark@....com>,
        Kees Cook <keescook@...omium.org>,
        "moderated list:XEN HYPERVISOR ARM" <xen-devel@...ts.xenproject.org>,
        "moderated list:ARM PORT" <linux-arm-kernel@...ts.infradead.org>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:MIPS" <linux-mips@...r.kernel.org>,
        "open list:XEN SWIOTLB SUBSYSTEM" <iommu@...ts.linux.dev>
Cc:     Roberto Sassu <roberto.sassu@...weicloud.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>, petr@...arici.cz
Subject: Re: [PATCH v4 1/8] swiotlb: make io_tlb_default_mem local to
 swiotlb.c

Hi Petr,

On 13/7/23 17:23, Petr Tesarik wrote:
> From: Petr Tesarik <petr.tesarik.ext@...wei.com>
> 
> SWIOTLB implementation details should not be exposed to the rest of the
> kernel. This will allow to make changes to the implementation without
> modifying non-swiotlb code.
> 
> To avoid breaking existing users, provide helper functions for the few
> required fields.
> 
> As a bonus, using a helper function to initialize struct device allows to
> get rid of an #ifdef in driver core.
> 
> Signed-off-by: Petr Tesarik <petr.tesarik.ext@...wei.com>
> ---
>   arch/arm/xen/mm.c          |  2 +-
>   arch/mips/pci/pci-octeon.c |  2 +-
>   arch/x86/kernel/pci-dma.c  |  2 +-
>   drivers/base/core.c        |  4 +---
>   drivers/xen/swiotlb-xen.c  |  2 +-
>   include/linux/swiotlb.h    | 25 +++++++++++++++++++++++-
>   kernel/dma/swiotlb.c       | 39 +++++++++++++++++++++++++++++++++++++-
>   7 files changed, 67 insertions(+), 9 deletions(-)


> diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
> index 4e52cd5e0bdc..07216af59e93 100644
> --- a/include/linux/swiotlb.h
> +++ b/include/linux/swiotlb.h
> @@ -110,7 +110,6 @@ struct io_tlb_mem {
>   	atomic_long_t used_hiwater;
>   #endif
>   };
> -extern struct io_tlb_mem io_tlb_default_mem;
>   
>   static inline bool is_swiotlb_buffer(struct device *dev, phys_addr_t paddr)
>   {
> @@ -128,13 +127,22 @@ static inline bool is_swiotlb_force_bounce(struct device *dev)
>   
>   void swiotlb_init(bool addressing_limited, unsigned int flags);
>   void __init swiotlb_exit(void);
> +void swiotlb_dev_init(struct device *dev);
>   size_t swiotlb_max_mapping_size(struct device *dev);
> +bool is_swiotlb_allocated(void);
>   bool is_swiotlb_active(struct device *dev);
>   void __init swiotlb_adjust_size(unsigned long size);
> +phys_addr_t default_swiotlb_start(void);
> +phys_addr_t default_swiotlb_limit(void);

Usually we use start/end, base/limit, low[est]/high[est] tuples.

Possibly clearer to rename, regardless:
Reviewed-by: Philippe Mathieu-Daudé <philmd@...aro.org>

> diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
> index 2b83e3ad9dca..873b077d7e37 100644
> --- a/kernel/dma/swiotlb.c
> +++ b/kernel/dma/swiotlb.c


> @@ -958,6 +975,26 @@ bool is_swiotlb_active(struct device *dev)
>   }
>   EXPORT_SYMBOL_GPL(is_swiotlb_active);
>   
> +/**
> + * default_swiotlb_start() - get the start of the default SWIOTLB
> + *
> + * Get the lowest physical address used by the default software IO TLB pool.
> + */
> +phys_addr_t default_swiotlb_start(void)
> +{
> +	return io_tlb_default_mem.start;
> +}
> +
> +/**
> + * default_swiotlb_limit() - get the highest address in the default SWIOTLB
> + *
> + * Get the highest physical address used by the default software IO TLB pool.

(note you describe lowest/highest).

> + */
> +phys_addr_t default_swiotlb_limit(void)
> +{
> +	return io_tlb_default_mem.end - 1;
> +}
> +
>   #ifdef CONFIG_DEBUG_FS
>   
>   static int io_tlb_used_get(void *data, u64 *val)