[PATCH] mmc: add option to skip eMMC deinit on OS handoff
=?ks_c_5601-1987?B?udq5zr/sIChNVyBQYXJrKQ==?= <[email protected]>
| Newsgroups | gmane.comp.boot-loaders.u-boot.general,gmane.comp.boot-loaders.u-boot |
|---|---|
| Message-ID | <SLXP216MB11482B060B2F37F28BD4A84DF0A32@SLXP216MB1148.KORP216.PROD.OUTLOOK.COM> |
When U-Boot hands off to the OS, mmc_deinit() renegotiates the bus down out of HS200/HS400 by issuing CMD6 switches and retuning, then changes the clock. For eMMC this is unnecessary: the OS issues CMD0 (card reset), which returns the device to backward-compatible mode, and renegotiates from scratch regardless of the mode U-Boot left the device in. Add a Kconfig option, MMC_SKIP_DEINIT, to skip this downgrade for eMMC devices. SD cards are always deinitialized: a UHS card switched to 1.8V signaling cannot be reset by CMD0 and needs a power cycle, which not every board can perform. This removes unnecessary CMD6 switches, retuning and clock changes from the OS-handoff path, which matters on fast-boot / automotive platforms. Signed-off-by: Minwoo Park <[email protected]> --- drivers/mmc/Kconfig | 23 +++++++++++++++++++++++ drivers/mmc/mmc.c | 3 +++ 2 files changed, 26 insertions(+) diff --git a/drivers/mmc/Kconfig b/drivers/mmc/Kconfig index 6c513328de2..8b516bf359f 100644 --- a/drivers/mmc/Kconfig +++ b/drivers/mmc/Kconfig @@ -226,6 +226,29 @@ config SPL_MMC_HS200_SUPPORT The HS200 mode is support by some eMMC. The bus frequency is up to 200MHz. This mode requires tuning the IO. +config MMC_SKIP_DEINIT + bool "Skip eMMC deinit on OS handoff" + depends on MMC_HS200_SUPPORT || MMC_HS400_SUPPORT + help + When U-Boot hands off to the OS, the MMC subsystem normally + renegotiates the bus down out of HS200/HS400 by issuing CMD6 + switches and retuning, then changes the clock. For eMMC this is + unnecessary: the OS issues CMD0 (card reset), which returns the + device to backward-compatible mode, and renegotiates from scratch + regardless of the mode U-Boot left the device in. + + Enabling this option skips the deinit for eMMC devices only. SD + cards are always deinitialized: a UHS card switched to 1.8V + signaling cannot be reset by CMD0 and needs a power cycle, which + not every board can perform. + + This removes unnecessary CMD6 switches, retuning and clock + changes from the OS-handoff path, which matters on fast-boot / + automotive platforms. + + If unsure, say N. If your eMMC device or controller cannot be + re-initialised by the OS out of HS200/HS400, say N. + config MMC_VERBOSE bool "Output more information about the MMC" default y diff --git a/drivers/mmc/mmc.c b/drivers/mmc/mmc.c index 2e565560656..121739a0a33 100644 --- a/drivers/mmc/mmc.c +++ b/drivers/mmc/mmc.c @@ -3184,6 +3184,9 @@ int mmc_deinit(struct mmc *mmc) return sd_select_mode_and_width(mmc, caps_filtered); } else { + if (CONFIG_IS_ENABLED(MMC_SKIP_DEINIT)) + return 0; + caps_filtered = mmc->card_caps & ~(MMC_CAP(MMC_HS_200) | MMC_CAP(MMC_HS_400) | MMC_CAP(MMC_HS_400_ES)); base-commit: ece349ade2973e220f524ce59e59711cc919263f -- 2.25.1 This email and any attachments to it may be confidential and are intended solely for the use of the individual to whom it is addressed. Any views or opinions expressed are solely those of the author and do not necessarily represent those of Telechips Inc. If you are not the intended recipient of this email, you must neither take any action based upon its contents nor copy or show it to anyone. Please notify the sender immediately by email if you have received this email by mistake and delete this email from your system. Please consider the environment before printing this email.
0001-mmc-add-option-to-skip-eMMC-deinit-on-OS-handoff.patch
(application/octet-stream, 3 KB)
From 24422be33228f3acbfb9b15b680d3808237f6a21 Mon Sep 17 00:00:00 2001 From: Minwoo Park <[email protected]> Date: Wed, 12 Aug 2026 11:47:27 +0900 Subject: [PATCH] mmc: add option to skip eMMC deinit on OS handoff When U-Boot hands off to the OS, mmc_deinit() renegotiates the bus down out of HS200/HS400 by issuing CMD6 switches and retuning, then changes the clock. For eMMC this is unnecessary: the OS issues CMD0 (card reset), which returns the device to backward-compatible mode, and renegotiates from scratch regardless of the mode U-Boot left the device in. Add a Kconfig option, MMC_SKIP_DEINIT, to skip this downgrade for eMMC devices. SD cards are always deinitialized: a UHS card switched to 1.8V signaling cannot be reset by CMD0 and needs a power cycle, which not every board can perform. This removes unnecessary CMD6 switches, retuning and clock changes from the OS-handoff path, which matters on fast-boot / automotive platforms. Signed-off-by: Minwoo Park <[email protected]> --- drivers/mmc/Kconfig | 23 +++++++++++++++++++++++ drivers/mmc/mmc.c | 3 +++ 2 files changed, 26 insertions(+) diff --git a/drivers/mmc/Kconfig b/drivers/mmc/Kconfig index 6c513328de2..8b516bf359f 100644 --- a/drivers/mmc/Kconfig +++ b/drivers/mmc/Kconfig @@ -226,6 +226,29 @@ config SPL_MMC_HS200_SUPPORT The HS200 mode is support by some eMMC. The bus frequency is up to 200MHz. This mode requires tuning the IO. +config MMC_SKIP_DEINIT + bool "Skip eMMC deinit on OS handoff" + depends on MMC_HS200_SUPPORT || MMC_HS400_SUPPORT + help + When U-Boot hands off to the OS, the MMC subsystem normally + renegotiates the bus down out of HS200/HS400 by issuing CMD6 + switches and retuning, then changes the clock. For eMMC this is + unnecessary: the OS issues CMD0 (card reset), which returns the + device to backward-compatible mode, and renegotiates from scratch + regardless of the mode U-Boot left the device in. + + Enabling this option skips the deinit for eMMC devices only. SD + cards are always deinitialized: a UHS card switched to 1.8V + signaling cannot be reset by CMD0 and needs a power cycle, which + not every board can perform. + + This removes unnecessary CMD6 switches, retuning and clock + changes from the OS-handoff path, which matters on fast-boot / + automotive platforms. + + If unsure, say N. If your eMMC device or controller cannot be + re-initialised by the OS out of HS200/HS400, say N. + config MMC_VERBOSE bool "Output more information about the MMC" default y diff --git a/drivers/mmc/mmc.c b/drivers/mmc/mmc.c index 2e565560656..121739a0a33 100644 --- a/drivers/mmc/mmc.c +++ b/drivers/mmc/mmc.c @@ -3184,6 +3184,9 @@ int mmc_deinit(struct mmc *mmc) return sd_select_mode_and_width(mmc, caps_filtered); } else { + if (CONFIG_IS_ENABLED(MMC_SKIP_DEINIT)) + return 0; + caps_filtered = mmc->card_caps & ~(MMC_CAP(MMC_HS_200) | MMC_CAP(MMC_HS_400) | MMC_CAP(MMC_HS_400_ES)); base-commit: ece349ade2973e220f524ce59e59711cc919263f -- 2.25.1