linux-kernel - Re: [PATCH v3] mmc: Avoid reprogram all keys to Inline Crypto Engine for MMC runtime suspend resume

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Message-ID: <a569a2c3-2fb2-4a40-8d54-898e7c36f4b3@oss.qualcomm.com>
Date: Fri, 18 Jul 2025 14:05:51 +0200
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Debraj Mukhopadhyay <quic_dmukhopa@...cinc.com>,
        Eric Biggers <ebiggers@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Adrian Hunter <adrian.hunter@...el.com>
Cc: linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, kernel@...cinc.com,
        Neeraj Soni <quic_neersoni@...cinc.com>,
        Ram Prakash Gupta <quic_rampraka@...cinc.com>,
        Nitin Rawat <quic_nitirawa@...cinc.com>,
        Sachin Gupta <quic_sachgupt@...cinc.com>,
        Bhaskar Valaboju <quic_bhaskarv@...cinc.com>,
        Gaurav Kashyap <quic_gaurkash@...cinc.com>,
        Sarthak Garg <quic_sartgarg@...cinc.com>
Subject: Re: [PATCH v3] mmc: Avoid reprogram all keys to Inline Crypto Engine
 for MMC runtime suspend resume

On 7/18/25 1:02 PM, Debraj Mukhopadhyay wrote:
> Crypto reprogram all keys is called for each MMC runtime
> suspend/resume in current upstream design. If this is implemented
> as a non-interruptible call to TEE for security, the cpu core is
> blocked for execution while this call executes although the crypto
> engine already has the keys. For example, glitches in audio/video
> streaming applications have been observed due to this. Add the flag
> MMC_CAP2_CRYPTO_NO_REPROG as part of host->caps2 to control reprogramming
> keys to crypto engine for socs which dont require this feature.
> 
> Signed-off-by: Seshu Madhavi Puppala <quic_spuppala@...cinc.com>
> Co-developed-by: Ram Prakash Gupta <quic_rampraka@...cinc.com>
> Signed-off-by: Ram Prakash Gupta <quic_rampraka@...cinc.com>
> Co-developed-by: Sarthak Garg <quic_sartgarg@...cinc.com>
> Signed-off-by: Sarthak Garg <quic_sartgarg@...cinc.com>
> Signed-off-by: Debraj Mukhopadhyay <quic_dmukhopa@...cinc.com>
> 
> ---

Let's take a step back - do we need to ever program this more than
once on QC? What about other devices (e.g. the generic cqhci-crypto)?
Do they also lose the crypto context over a runtime pm cycle?

If our hardware is fine with set-it-and-forget-it approach, maybe
we could limit this to a small if-condition sdhci-msm.c

[...]

> @@ -459,6 +459,11 @@ struct mmc_host {
>  #define MMC_CAP2_CRYPTO		0
>  #endif
>  #define MMC_CAP2_ALT_GPT_TEGRA	(1 << 28)	/* Host with eMMC that has GPT entry at a non-standard location */
> +#ifdef CONFIG_MMC_CRYPTO
> +#define MMC_CAP2_CRYPTO_NO_REPROG	(1 << 29)	/* Host handles inline crypto key reprogramming */
> +#else
> +#define MMC_CAP2_CRYPTO_NO_REPROG	0
> +#endif
This (and the crypto ifdef for MMC_CAP2_CRYPTO) looks like unnecessary
churn - crypto functions should never be called if the config is disabled
in the first place

Konrad