Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH v1] partitions/efi: Add 'gpt_sector' kernel cmdline
 parameter
To:     Christoph Hellwig <hch@infradead.org>
Cc:     Jens Axboe <axboe@kernel.dk>, Davidlohr Bueso <dave@stgolabs.net>,
        Colin Cross <ccross@android.com>,
        Thierry Reding <thierry.reding@gmail.com>,
        Jonathan Hunter <jonathanh@nvidia.com>,
        =?UTF-8?B?TWljaGHFgiBNaXJvc8WCYXc=?= <mirq-linux@rere.qmqm.pl>,
        David Heidelberg <david@ixit.cz>,
        Peter Geis <pgwipeout@gmail.com>, linux-efi@vger.kernel.org,
        linux-tegra@vger.kernel.org, linux-block@vger.kernel.org,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20200219162339.16192-1-digetx@gmail.com>
 <20200219162738.GA10644@infradead.org>
From:   Dmitry Osipenko <digetx@gmail.com>
Message-ID: <d0df41ca-e14a-1bbf-5632-781d3e46f279@gmail.com>
Date:   Wed, 19 Feb 2020 19:38:30 +0300
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101
 Thunderbird/68.3.0
MIME-Version: 1.0
In-Reply-To: <20200219162738.GA10644@infradead.org>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

19.02.2020 19:27, Christoph Hellwig пишет:
> 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.

I'll try to take a look at RE, pretty sure somebody tried to do that before.