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Date:   Fri, 22 Jul 2022 11:58:59 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc:     Robert Beckett <bob.beckett@collabora.com>,
        Jani Nikula <jani.nikula@linux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@intel.com>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>, kernel@collabora.com,
        Christoph Hellwig <hch@lst.de>,
        Thomas Hellstrom <thomas.hellstrom@intel.com>,
        Matthew Auld <matthew.auld@intel.com>,
        intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] drm/i915: stop using swiotlb
Message-ID: <20220722095859.GB14113@lst.de>
References: <20220721174307.1085741-1-bob.beckett@collabora.com> <a0a7a734-d3dd-960e-f130-39f86b04b24d@linux.intel.com>
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On Fri, Jul 22, 2022 at 10:45:54AM +0100, Tvrtko Ursulin wrote:
>> -	unsigned int size = swiotlb_max_segment();
>> -
>> -	if (size == 0)
>> -		size = UINT_MAX;
>
> On a more detailed look, there was a CI failure which makes me think this 
> cap might need to stay. Because max sg segment is unsigned int. So I wonder 
> if sg contstruction overflows without it.
>
> If this quick analysis is right, you could leave i915_sg_segment_size 
> helper and cap the return from dma_max_mapping_size to UINT_MAX in it.

As dma_max_mapping_size retuns a size_t it would be good to make
all variables using it a size_t as well.  In places where that gets
lower to an unsigned int your probably want this cap.