The STM32 SDMMC peripheral (at least for the STM32F429, STM32F469 and STM32F746, which are all the currently supported devices using periphid 0x00880180) requires DMA to be performed in peripheral flow controller mode. From the STM32F74/5 reference manual, section 35.3.2: "SDMMC host allows only to use the DMA in peripheral flow controller mode. DMA stream used to serve SDMMC must be configured in peripheral flow controller mode" This patch adds a variant option to control peripheral flow control and enables it for the STM32 variant. Signed-off-by: Ben Wolsieffer <Ben.Wolsieffer@hefring.com> Reviewed-by: Linus Walleij <linus.walleij@linaro.org> Link: https://lore.kernel.org/r/20230928135644.1489691-1-ben.wolsieffer@hefring.com Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>