d6743a8a1a
Per SD specification physical layer v4.0, section 3.9.4, it says "UHS-I supports only 4-bit mode. Host shall select 4-bit mode by ACMD6. However mmc_sd_init_uhs_card() still go ahead to initialize the cards anyway, whether card or host won't support 4-bit mode. This breaks the platforms which could support UHS-I mode but on some certain boards only support 1-bit mode with a UHS-I card inserted, as all the tuning process is broken due to this. Alternatively, we should check the return value from mmc_set_bus_width() to see if host could finish the request to switch the bus width on its side. But that needs more thing to do than this patch that just bails out early to try high speed mode if 4-bit mode isn't available for whatever reason. And this patch could also fix the same problem for sdio since R4_18V_PRESENT won't be set for ocr when mmc_sdio_init_card() finds mmc_host_uhs() is false. Note that this patch doesn't keep the checking of card->scr.sda_spec3 and comparing card->scr.bus_widths with SD_SCR_BUS_WIDTH_4 within mmc_sd_init_uhs_card() since if the sd cards response with SD_ROCR_S18A, it definitely supports UHS-I mode, which implicitly means these checkings are always true. Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com> Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org> |
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README
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.