Hi, On Wed, May 11, 2016 at 2:40 PM, Douglas Anderson <dianders@xxxxxxxxxxxx> wrote: > 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. > > Let's explicitly set this phase in the kernel. > > 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: > * 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. > > Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx> > --- > Changes in v2: > - Now use 90 degrees for some modes; updated comments to say why. > > drivers/mmc/host/dw_mmc-rockchip.c | 64 ++++++++++++++++++++++++++++++++++++++ > 1 file changed, 64 insertions(+) Just a note that I have since found out that recent patches in the kernel in fact _do_ init the drive phase and apparently do it improperly. That means that $SUBJECT patch actually is expected to fix real problems on real devices. See <https://patchwork.kernel.org/patch/9085311/> for some details. -Doug -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
