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Date:   Mon, 9 Sep 2019 18:13:31 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Thierry Reding <thierry.reding@gmail.com>
Cc:     Jens Axboe <axboe@kernel.dk>, Ulf Hansson <ulf.hansson@linaro.org>,
        Adrian Hunter <adrian.hunter@intel.com>,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>,
        Christoph Hellwig <hch@lst.de>,
        Simon Horman <horms+renesas@verge.net.au>,
        Jon Hunter <jonathanh@nvidia.com>, linux-block@vger.kernel.org,
        linux-mmc@vger.kernel.org, linux-tegra@vger.kernel.org
Subject: Re: [PATCH 1/3] block: Respect the device's maximum segment size
Message-ID: <20190909161331.GA19650@lst.de>
References: <20190909125658.30559-1-thierry.reding@gmail.com> <20190909125658.30559-2-thierry.reding@gmail.com>
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On Mon, Sep 09, 2019 at 02:56:56PM +0200, Thierry Reding wrote:
> From: Thierry Reding <treding@nvidia.com>
> 
> When enabling the DMA map merging capability for a queue, ensure that
> the maximum segment size does not exceed the device's limit.

We can't do that unfortunately.  If we use the virt_boundary setting
we do aggressive merges that there is no accounting for.  So we can't
limit the segment size.

And at least for the case how devices usually do the addressing
(page based on not sgl based) that needs the virt_boundary there isn't
really any concept like a segment anyway.