summaryrefslogtreecommitdiff
path: root/Documentation
diff options
context:
space:
mode:
authorDouglas Anderson <dianders@chromium.org>2016-05-12 11:31:50 -0700
committerUlf Hansson <ulf.hansson@linaro.org>2016-05-23 11:45:47 +0200
commitd4aa908c7978f60557a799ca53b5ae4166fd8355 (patch)
treeea02d8c1fb6f78de87e57cd5b6180eda84724da2 /Documentation
parent225faf871ec24f3fa6daa4d2324b5de56690e1c5 (diff)
mmc: dw_mmc: rockchip: Set the drive phase properly
Historically for Rockchip devices we've relied on the power-on default (or perhaps the firmware setting) to get the correct drive phase for dw_mmc devices. This worked OK for the most part, but: * Relying on the setting just "being right" is a bit fragile. * As soon as there is an instance where the power on default is wrong or where the firmware didn't configure this properly then we'll get a mysterious failure. In commit 7a03fe6f48f3 ("clk: rockchip: reset init state before mmc card initialization") we actually started setting this explicitly in the kernel, but that commit wasn't quite right and also wasn't quite enough. See <https://patchwork.kernel.org/patch/9085311/> for some details. Let's explicitly set this phase in dw_mmc. The comments inside this patch try to explain the situation quite throughly, but the high level overview of this is: Before this patch on rk3288 devices tested (after revert of the clock patch described above): * eMMC: 180 degrees * SDMMC/SDIO0/SDIO1: 90 degrees After this patch: * Use 90 degree phase offset usually. * Use 180 degree phase offset for MMC_DDR52, SDR104, HS200. That means we are _changing_ behavior for those devices in this way: * If we have HS200 eMMC or DDR52 eMMC, we'll run ID mode at 90 degrees (vs 180) but otherwise have no change. * For any non-HS200 / non-DDR52 eMMC devices we'll now _always_ run at 90 degrees (vs 180). It seems fairly unlikely that building modern hardware is using an eMMC that isn't using DDR52 or HS200, of course. * For SDR104 cards we'll now run with 180 degree phase offset (vs 90). It's expected that 90 degree phase offset would have worked OK, but this gives us extra margin. I have tested this by inserting my collection of uSD cards (mostly UHS, though a few not) into a veyron_minnie and confirmed that they still seem to enumerate properly. For a subset of them I tried putting a filesystem on them and also tried running mmc_test. Fixes: 7a03fe6f48f3 ("clk: rockchip: reset init state before mmc card initialization") Signed-off-by: Douglas Anderson <dianders@chromium.org> Reviewed-by: Shawn Lin <shawn.lin@rock-chips.com> Tested-by: Heiko Stuebner <heiko@sntech.de> Tested-by: Enric Balletbo i Serra <enric.balletbo@collabora.com> Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com> Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Diffstat (limited to 'Documentation')
0 files changed, 0 insertions, 0 deletions