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

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Date: Wed, 6 Mar 2024 15:38:33 +0100
From: Linus Walleij <linus.walleij@...aro.org>
To: "Jorge Ramirez-Ortiz, Foundries" <jorge@...ndries.io>
Cc: Jens Wiklander <jens.wiklander@...aro.org>, Tomas Winkler <tomas.winkler@...el.com>, 
	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 3:22 PM Jorge Ramirez-Ortiz, Foundries
<jorge@...ndries.io> wrote:

> I still cant grasp how "target_part = idata->rpmb->part_index" is
> helping in the design.
>
> What happens when:
> 1) EXT_CSD_PART_CONFIG_ACC_MASK > part_index > EXT_CSD_PART_CONFIG_ACC_RPMB
> target_part now could be indicating a GP instead of an RPMB leading to failures.
>
> 2) part_index <= EXT_CSD_PART_CONFIG_ACC_RPMB
> loses the part_index value .
>
> So part_index should be larger than EXT_CSD_PART_CONFIG_ACC_MASK even
> though the comment indicates it starts at 0?
>
> /**
>  * struct mmc_rpmb_data - special RPMB device type for these areas
>  * @dev: the device for the RPMB area
>  * @chrdev: character device for the RPMB area
>  * @id: unique device ID number
>  * @part_index: partition index (0 on first)    <---------------------
>  * @md: parent MMC block device
>  * @node: list item, so we can put this device on a list
>  */
> struct mmc_rpmb_data {
>         struct device dev;
>         struct cdev chrdev;
>         int id;
>
> is it just possible that "target_part = idata->rpmb->part_index" just
> needs to be shifted to avoid issues?
>
> I think the fix to the regression I introduced could perhaps address
> this as well.

I have no clue how the regression happened really ... heh.

We should probably rename it part_cfg because that is what we
store in it, it's assigned from card->part[idx].part_cfg.

Then the id field in mmc_rpmb_data should be deleted along
with all the IDA counter code etc and the partition name hardcoded
to be "0" as there will never be anything else.

Yours,
Linus Walleij