linux-kernel - Re: [PATCH v1] partitions/efi: Add 'gpt

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Message-ID: <20200219162738.GA10644@infradead.org>
Date:   Wed, 19 Feb 2020 08:27:38 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Jens Axboe <axboe@...nel.dk>, Davidlohr Bueso <dave@...olabs.net>,
        Colin Cross <ccross@...roid.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Michał Mirosław <mirq-linux@...e.qmqm.pl>,
        David Heidelberg <david@...t.cz>,
        Peter Geis <pgwipeout@...il.com>, linux-efi@...r.kernel.org,
        linux-tegra@...r.kernel.org, linux-block@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] partitions/efi: Add 'gpt_sector' kernel cmdline
 parameter

On Wed, Feb 19, 2020 at 07:23:39PM +0300, Dmitry Osipenko wrote:
> The gpt_sector=<sector> causes the GPT partition search to look at the
> specified sector for a valid GPT header if the GPT is not found at the
> beginning or the end of block device.
> 
> In particular this is needed for NVIDIA Tegra consumer-grade Android
> devices in order to make them usable with the upstream kernel because
> these devices use a proprietary / closed-source partition table format
> for the EMMC and it's impossible to change the partition's format. Luckily
> there is a GPT table in addition to the proprietary table, which is placed
> in uncommon location of the EMMC storage and bootloader passes the
> location to kernel using "gpt gpt_sector=<sector>" cmdline parameters.
> 
> This patch is based on the original work done by Colin Cross for the
> downstream Android kernel.

I don't think a magic command line is the way to go.  The best would be
to reverse-engineer the proprietary partition table format.  If that is
too hard we can at least key off the odd GPT location based of it's
magic number.