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mmc: sunxi: Clarify new timing mode usage and implementation
Newer sunxi mmc controller variants support what they call the "new timing mode". Support for this was implemented in two ways, according to the hardware that was seen at the time. The first type retained the old timing mode, and both the clock and mmc controllers had switches to select which mode was used. Both switches had to be set to the same setting. This variant was denoted with the .has_timings_switch field in the sunxi_mmc_cfg structure. This hardware is only seen on the A83T. The second type did away with the old timing mode. The clock controller no longer had the mode selection or clock delay setting bits. In some cases the mmc controller retained its mode selection bit, but this always needed to be set to the new mode, or instabilities would occur. In a few cases, such as the A64 and H6 eMMC controller, the mode selection bit is gone, but the controller still behaves like the new timing mode, requiring the module clock to be double the card clock in DDR transfer modes. This variant is denoted with the .needs_new_timings field. This patch adds more comments explaining the two fields, as well as the possibly nonexistent mode switch in the mmc controller. The .has_timings_switch is renamed to .ccu_has_timings_switch to clarify its meaning. Signed-off-by:Chen-Yu Tsai <wens@csie.org> Acked-by: