linux-kernel - Re: [PATCH] mmc: part_switch: fixes switch on gp3 partition

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Message-ID: <CACRpkdYZrDgVVCp2bqJqY1BpeHSXDWbRSqk6d=N_QhC4OVv=Ew@mail.gmail.com>
Date: Wed, 6 Mar 2024 14:18:49 +0100
From: Linus Walleij <linus.walleij@...aro.org>
To: "Jorge Ramirez-Ortiz, Foundries" <jorge@...ndries.io>, Jens Wiklander <jens.wiklander@...aro.org>, 
	Tomas Winkler <tomas.winkler@...el.com>
Cc: Dominique Martinet <asmadeus@...ewreck.org>, Ulf Hansson <ulf.hansson@...aro.org>, 
	linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Dominique Martinet <dominique.martinet@...ark-techno.com>, stable@...r.kernel.org
Subject: Re: [PATCH] mmc: part_switch: fixes switch on gp3 partition

On Wed, Mar 6, 2024 at 10:05 AM Jorge Ramirez-Ortiz, Foundries
<jorge@...ndries.io> wrote:

> That looked strange as there should be support for 4 GP but this code
> kind of convinced me of the opposite.
>
>         if (idata->rpmb) {
>                 /* Support multiple RPMB partitions */
>                 target_part = idata->rpmb->part_index;
>                 target_part |= EXT_CSD_PART_CONFIG_ACC_RPMB;
>         }
>
> So if we apply the fix that you propose, how are multiple RPMB
> partitions (ie, 4) going to be identified as RPMB? Unless there can't be
> more than 3?

As far as I can tell there can only be one RPMB partition per device.

The v5.1A spec says (section 6.2.1):

"Two Boot Area Partitions, (...)"
"One RPMB Partition accessed through a trusted mechanism, (...)"
"Four General Purpose Area Partitions (...)"

implying there can be only one RPMB.

Also I have never seen more than one in practice.

I paged in Jens Wiklander and Tomas Winkler who used it much more
than I have, to confirm.

I think my linked list of RPMB partitions is a case of overdesign
and could be simplified. I blame the fact that I didn't have the
(non-public) spec at the time.

Yours,
Linus Walleij