linux-kernel - Re: [RFC][PATCH] mmc_block: Allow more than 8 partitions per card

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Date:	Fri, 16 Oct 2015 12:31:01 -0700
From:	John Stultz <john.stultz@...aro.org>
To:	Austin S Hemmelgarn <ahferroin7@...il.com>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Colin Cross <ccross@...roid.com>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Ben Hutchings <ben@...adent.org.uk>,
	Chuanxiao Dong <chuanxiao.dong@...el.com>,
	Shawn Lin <shawn.lin@...k-chips.com>,
	Android Kernel Team <kernel-team@...roid.com>,
	linux-mmc <linux-mmc@...r.kernel.org>
Subject: Re: [RFC][PATCH] mmc_block: Allow more than 8 partitions per card

On Fri, Oct 16, 2015 at 12:03 PM, Austin S Hemmelgarn
<ahferroin7@...il.com> wrote:
> On 2015-10-16 14:40, John Stultz wrote:
>>
>> From: Colin Cross <ccross@...roid.com>
>>
>> It is quite common for Android devices to utilize more
>> then 8 partitions on internal eMMC storage. This patch,
>> which has been carried for quite awhile in the AOSP common
>> tree is necessary in order to support such configurations,
>> so I wanted to submit it for consideration upstream.
>
> Isn't this what CONFIG_MMC_BLOCK_MINORS is for?  It does limit you to 256
> minors total, and therefore the number of supported MMC's is equal to
> 256/CONFIG_MMC_BLOCK_MINORS, but I've never heard of an Android device with
> support for more than 4 MMC/SD cards (including eMMC's), and I would
> seriously question anyone who has the need for more than 32 partitions on
> the root device for a phone/tablet/television.

So thanks, CONFIG_MMC_BLOCK_MINORS is something I wasn't aware of, and
it does seem to allow me to boot on my device w/o the proposed patch!

That said, my fairly old device does have 30-partitions now, and from
Linux Plumber's[1] it seems like Android devices are only going to
have more partitions in the future. So as Arnd commented, if the
proposed patch provides a less limited solution, it might still be
worth consideration.  I'll give it a day or so for folks to provide
any more commentary, and if no other objections are brought up, I'll
re-submit with an improve rational for the patch that includes this
info.

Thanks for the feedback!
-john

[1]: https://linuxplumbersconf.org/2015/ocw//system/presentations/3387/original/Android%20system,%20partitions%20and%20customization.pdf
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