Re: [PATCH 03/11] swiotlb: simplify swiotlb_max_segment

From: Anshuman Khandual <anshuman.khandual@arm.com>
To: Christoph Hellwig <hch@lst.de>, iommu@lists.linux-foundation.org
Cc: x86@kernel.org, Stefano Stabellini <sstabellini@kernel.org>,
	Boris Ostrovsky <boris.ostrovsky@oracle.com>,
	Juergen Gross <jgross@suse.com>, Joerg Roedel <joro@8bytes.org>,
	David Woodhouse <dwmw2@infradead.org>,
	Lu Baolu <baolu.lu@linux.intel.com>,
	Robin Murphy <robin.murphy@arm.com>,
	linux-arm-kernel@lists.infradead.org,
	xen-devel@lists.xenproject.org, linux-ia64@vger.kernel.org,
	linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
	linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org,
	linux-hyperv@vger.kernel.org, tboot-devel@lists.sourceforge.net,
	linux-pci@vger.kernel.org
Subject: Re: [PATCH 03/11] swiotlb: simplify swiotlb_max_segment
Date: Thu, 24 Feb 2022 16:04:02 +0530	[thread overview]
Message-ID: <9ef33986-eba0-01ee-28b6-1104e60c313d@arm.com> (raw)
In-Reply-To: <20220222153514.593231-4-hch@lst.de>


On 2/22/22 9:05 PM, Christoph Hellwig wrote:
> Remove the bogus Xen override that was usually larger than the actual
> size and just calculate the value on demand.  Note that
> swiotlb_max_segment still doesn't make sense as an interface and should
> eventually be removed.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  drivers/xen/swiotlb-xen.c |  2 --
>  include/linux/swiotlb.h   |  1 -
>  kernel/dma/swiotlb.c      | 20 +++-----------------
>  3 files changed, 3 insertions(+), 20 deletions(-)
> 
> diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
> index 47aebd98f52f5..485cd06ed39e7 100644
> --- a/drivers/xen/swiotlb-xen.c
> +++ b/drivers/xen/swiotlb-xen.c
> @@ -202,7 +202,6 @@ int xen_swiotlb_init(void)
>  	rc = swiotlb_late_init_with_tbl(start, nslabs);
>  	if (rc)
>  		return rc;
> -	swiotlb_set_max_segment(PAGE_SIZE);
>  	return 0;
>  error:
>  	if (nslabs > 1024 && repeat--) {
> @@ -254,7 +253,6 @@ void __init xen_swiotlb_init_early(void)
>  
>  	if (swiotlb_init_with_tbl(start, nslabs, true))
>  		panic("Cannot allocate SWIOTLB buffer");
> -	swiotlb_set_max_segment(PAGE_SIZE);
>  }
>  #endif /* CONFIG_X86 */
>  
> diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
> index f6c3638255d54..9fb3a568f0c51 100644
> --- a/include/linux/swiotlb.h
> +++ b/include/linux/swiotlb.h
> @@ -164,7 +164,6 @@ static inline void swiotlb_adjust_size(unsigned long size)
>  #endif /* CONFIG_SWIOTLB */
>  
>  extern void swiotlb_print_info(void);
> -extern void swiotlb_set_max_segment(unsigned int);
>  
>  #ifdef CONFIG_DMA_RESTRICTED_POOL
>  struct page *swiotlb_alloc(struct device *dev, size_t size);
> diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
> index 36fbf1181d285..519e363097190 100644
> --- a/kernel/dma/swiotlb.c
> +++ b/kernel/dma/swiotlb.c
> @@ -75,12 +75,6 @@ struct io_tlb_mem io_tlb_default_mem;
>  
>  phys_addr_t swiotlb_unencrypted_base;
>  
> -/*
> - * Max segment that we can provide which (if pages are contingous) will
> - * not be bounced (unless SWIOTLB_FORCE is set).
> - */
> -static unsigned int max_segment;
> -
>  static unsigned long default_nslabs = IO_TLB_DEFAULT_SIZE >> IO_TLB_SHIFT;
>  
>  static int __init
> @@ -104,18 +98,12 @@ early_param("swiotlb", setup_io_tlb_npages);
>  
>  unsigned int swiotlb_max_segment(void)
>  {
> -	return io_tlb_default_mem.nslabs ? max_segment : 0;
> +	if (!io_tlb_default_mem.nslabs)
> +		return 0;
> +	return rounddown(io_tlb_default_mem.nslabs << IO_TLB_SHIFT, PAGE_SIZE);
>  }
>  EXPORT_SYMBOL_GPL(swiotlb_max_segment);
>  
> -void swiotlb_set_max_segment(unsigned int val)
> -{
> -	if (swiotlb_force == SWIOTLB_FORCE)
> -		max_segment = 1;
> -	else
> -		max_segment = rounddown(val, PAGE_SIZE);
> -}
> -
>  unsigned long swiotlb_size_or_default(void)
>  {
>  	return default_nslabs << IO_TLB_SHIFT;
> @@ -267,7 +255,6 @@ int __init swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose)
>  
>  	if (verbose)
>  		swiotlb_print_info();
> -	swiotlb_set_max_segment(mem->nslabs << IO_TLB_SHIFT);
>  	return 0;
>  }
>  
> @@ -368,7 +355,6 @@ swiotlb_late_init_with_tbl(char *tlb, unsigned long nslabs)
>  	swiotlb_init_io_tlb_mem(mem, virt_to_phys(tlb), nslabs, true);
>  
>  	swiotlb_print_info();
> -	swiotlb_set_max_segment(mem->nslabs << IO_TLB_SHIFT);
>  	return 0;
>  }
>  

Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>