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Some boards have SD card connectors where the power rail cannot be switched off by the driver. However there are various circumstances when a card might be re-initialized, such as after system resume, warm re-boot, or error handling. However, a UHS card will continue to use 1.8V signaling unless it is power cycled. If the card has not been power cycled, it may still be using 1.8V signaling. According to the SD spec., the Bus Speed Mode (function group 1) bits 2 to 4 are zero if the card is initialized at 3.3V signal level. Thus they can be used to determine if the card has already switched to 1.8V signaling. Detect that situation and try to initialize a UHS-I (1.8V) transfer mode. Tested with the following cards: Transcend 4GB High Speed Kingston 64GB SDR104 Lexar by Micron HIGH-PERFORMANCE 300x 16GB DDR50 SanDisk Ultra 8GB DDR50 Transcend Ultimate 600x 16GB SDR104 Transcend Premium 300x 64GB SDR104 Lexar by Micron Professional 1000x 32GB UHS-II SDR104 SanDisk Extreme Pro 16GB SDR104 Signed-off-by: Adrian Hunter <adrian.hunter@intel.com> Tested-by: Zhoujie Wu <zjwu@marvell.com> Reviewed-by: Shawn Lin <shawn.lin@rock-chips.com> Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.