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From: Catalin Marinas <catalin.marinas@arm.com>
To: Jisheng Zhang <jszhang@marvell.com>
Cc: will.deacon@arm.com, linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	Arnd Bergmann <arnd@arndb.de>
Subject: Re: [PATCH] arm64: mm: only initialize swiotlb when necessary
Date: Wed, 8 Jun 2016 13:08:29 +0100	[thread overview]
Message-ID: <20160608120829.GB16322@e104818-lin.cambridge.arm.com> (raw)
In-Reply-To: <1465372426-4077-1-git-send-email-jszhang@marvell.com>

On Wed, Jun 08, 2016 at 03:53:46PM +0800, Jisheng Zhang wrote:
>  static int __init arm64_dma_init(void)
>  {
> +	if (swiotlb_force || max_pfn > (arm64_dma_phys_limit >> PAGE_SHIFT))
> +		swiotlb = 1;
> +
>  	return atomic_pool_init();
>  }

So any platform with RAM larger than 4GB would still initialise swiotlb.
I wouldn't say it's an issue, 64MB is not a significant loss on such
systems.

An alternative would be to defer the freeing until we are aware of all
possible dma masks for the populated devices (e.g. from DT), though I'm
not sure that's enough, drivers may try to change such masks when
probed.

-- 
Catalin

  parent reply	other threads:[~2016-06-08 12:08 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-08  7:53 [PATCH] arm64: mm: only initialize swiotlb when necessary Jisheng Zhang
2016-06-08  8:01 ` Jisheng Zhang
2016-06-08 12:08 ` Catalin Marinas [this message]
2016-06-08 15:49   ` Arnd Bergmann
2016-06-21 16:06     ` Catalin Marinas
2016-06-21 20:13       ` Arnd Bergmann
2016-06-22 16:56         ` Catalin Marinas
2016-06-08 12:13 ` Catalin Marinas
2016-06-12  7:14   ` Jisheng Zhang

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