Subject: Re: [LKML] [RFC PATCH v3 05/11] swiotlb: add swiotlb_set_default_size()

From: Konrad Rzeszutek Wilk <[email-masked]>
Date: Mon, 8 Mar 2010 11:59:40 -0500

On Sun, Mar 07, 2010 at 01:11:46PM +0100, Albert Herranz wrote:
> The current SWIOTLB code uses a default of 64MB for the IO TLB area.
> This size can be influenced using a kernel command line parameter "swiotlb".
> Unfortunately, the parsing of the kernel command line is done _after_ the
> swiotlb is initialized on some architectures.

Why can't it be moved up? I mean move the parsing of the kernel
parameters before the PCI subsystem?
> 
> This patch adds a new function swiotlb_set_default_size() which can be used
> before swiotlb_init() to indicate the desired IO TLB area size in bytes.
> 
> This will be used later to implement a smaller IO TLB on the Nintendo Wii
> video game console which just comes with 24MB + 64MB of RAM.

Use the io_tlb_nslabs, which is what swiotlb_init_with_default_size uses
(the passed in argument is only used if io_tlb_nslabs is not set).

> 
> Signed-off-by: Albert Herranz <[email-masked]>
> CC: [email-masked]
> CC: [email-masked]
> CC: [email-masked]
> CC: [email-masked]
> ---
>  include/linux/swiotlb.h |    2 ++
>  lib/swiotlb.c           |   27 ++++++++++++++++++++++++++-
>  2 files changed, 28 insertions(+), 1 deletions(-)
> 
> diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
> index 3954228..2af6a45 100644
> --- a/include/linux/swiotlb.h
> +++ b/include/linux/swiotlb.h
> @@ -22,6 +22,8 @@ extern int swiotlb_force;
>   */
>  #define IO_TLB_SHIFT 11
>  
> +extern size_t __init swiotlb_set_default_size(size_t size);
> +
>  extern void swiotlb_init(int verbose);
>  
>  extern void *swiotlb_alloc_boot(size_t bytes, unsigned long nslabs);
> diff --git a/lib/swiotlb.c b/lib/swiotlb.c
> index 8f2dad9..c99512d 100644
> --- a/lib/swiotlb.c
> +++ b/lib/swiotlb.c
> @@ -73,6 +73,11 @@ static char *io_tlb_start, *io_tlb_end;
>  static unsigned long io_tlb_nslabs;
>  
>  /*
> + * Default size for the IO TLB (64MB).
> + */
> +static __initdata size_t io_tlb_default_size = 64 * (1<<20);
> +
> +/*
>   * When the IOMMU overflows we return a fallback buffer. This sets the size.
>   */
>  static unsigned long io_tlb_overflow = 32*1024;
> @@ -117,6 +122,26 @@ setup_io_tlb_npages(char *str)
>  __setup("swiotlb=", setup_io_tlb_npages);
>  /* make io_tlb_overflow tunable too? */
>  
> +/**
> + * swiotlb_set_default_size() - set the default size for the IO TLB
> + * @size:	size in bytes of the IO TLB
> + *
> + * A platform can use this function to change the default size of the
> + * IO TLB when the default of 64MB is not suitable.
> + * This function must be called before swiotlb_init().
> + *
> + * Note that on some platforms this is the only way to influence the
> + * size of the IO TLB, as the command line may be parsed _after_ the
> + * IO TLB is initialized.
> + */
> +size_t __init swiotlb_set_default_size(size_t size)
> +{
> +	size_t previous_size = io_tlb_default_size;
> +
> +	io_tlb_default_size = size;
> +	return previous_size;
> +}
> +
>  void * __weak __init swiotlb_alloc_boot(size_t size, unsigned long nslabs)
>  {
>  	return alloc_bootmem_low_pages(size);
> @@ -193,7 +218,7 @@ swiotlb_init_with_default_size(size_t default_size, int verbose)
>  void __init
>  swiotlb_init(int verbose)
>  {
> -	swiotlb_init_with_default_size(64 * (1<<20), verbose);	/* default to 64MB */
> +	swiotlb_init_with_default_size(io_tlb_default_size, verbose);
>  }
>  
>  /*
> -- 
> 1.6.3.3
> 
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