linux-kernel - Re: [PATCH] mmc: core: Remove FW revision from CID check

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Date:   Tue, 18 Jul 2023 09:13:39 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Wenchao Chen <wenchao.chen@...soc.com>, ulf.hansson@...aro.org
Cc:     linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org,
        wenchao.chen666@...il.com, zhenxiong.lai@...soc.com,
        chunyan.zhang@...soc.com, yuelin.tang@...soc.com
Subject: Re: [PATCH] mmc: core: Remove FW revision from CID check

On 18/07/23 04:15, Wenchao Chen wrote:
> When the card is reset, mmc_card_init() will check if this
> card is the previous card by comparing the CID.
> 
> If the firmware is upgraded, the product version may change,
> so we remove the product version from the CID check.

What is the use-case for this?  I would have thought it is safer
not to assume anything about the card after the firmware has been
upgraded.

> 
> Signed-off-by: Wenchao Chen <wenchao.chen@...soc.com>
> ---
>  drivers/mmc/core/mmc.c | 18 +++++++++++++++++-
>  1 file changed, 17 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
> index 89cd48fcec79..32a73378d5c3 100644
> --- a/drivers/mmc/core/mmc.c
> +++ b/drivers/mmc/core/mmc.c
> @@ -32,6 +32,9 @@
>  #define MIN_CACHE_EN_TIMEOUT_MS 1600
>  #define CACHE_FLUSH_TIMEOUT_MS 30000 /* 30s */
>  
> +#define MMC_CID_PRV_MASK GENMASK(23, 16)
> +#define MMC_CID_CRC_MASK GENMASK(7, 0)
> +
>  static const unsigned int tran_exp[] = {
>  	10000,		100000,		1000000,	10000000,
>  	0,		0,		0,		0
> @@ -126,6 +129,19 @@ static int mmc_decode_cid(struct mmc_card *card)
>  	return 0;
>  }
>  
> +static int mmc_check_cid(u32 *cid, u32 *raw_cid)
> +{
> +	/*
> +	 * When comparing CID, we need to remove the product
> +	 * version (Field PRV, offset 55:48) and CRC. Because
> +	 * the product version will change when the firmware
> +	 * is upgraded. Also, the new CRC is different.
> +	 */
> +	return cid[0] != raw_cid[0] || cid[1] != raw_cid[1] ||
> +		(cid[2] & ~MMC_CID_PRV_MASK) != (raw_cid[2] & ~MMC_CID_PRV_MASK) ||
> +		(cid[3] & ~MMC_CID_CRC_MASK) != (raw_cid[3] & ~MMC_CID_CRC_MASK);
> +}
> +
>  static void mmc_set_erase_size(struct mmc_card *card)
>  {
>  	if (card->ext_csd.erase_group_def & 1)
> @@ -1640,7 +1656,7 @@ static int mmc_init_card(struct mmc_host *host, u32 ocr,
>  		goto err;
>  
>  	if (oldcard) {
> -		if (memcmp(cid, oldcard->raw_cid, sizeof(cid)) != 0) {
> +		if (mmc_check_cid(cid, oldcard->raw_cid)) {
>  			pr_debug("%s: Perhaps the card was replaced\n",
>  				mmc_hostname(host));
>  			err = -ENOENT;