Allwinner's mmc controller supports signal voltage switching. This is
supported in code in Allwinner's kernel. However, publicly available
boards all tie it to a fixed 3.0/3.3V regulator, with options to tie
it to 1.8V for eMMC on some.
Since Allwinner's kernel is an ancient 3.4, it is hard to say whether
adapting it's code to a modern mainline kernel would work. Block signal
voltage switching until someone has proper hardware to implement and
test this.
This only affects SD UHS-1 modes, as eMMC switches the voltage directly
without any signaling.
Signed-off-by: Chen-Yu Tsai <w...@csie.org>
---
drivers/mmc/host/sunxi-mmc.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)
diff --git a/drivers/mmc/host/sunxi-mmc.c b/drivers/mmc/host/sunxi-mmc.c
index 790f01662b4e..0495ae7da6d6 100644
--- a/drivers/mmc/host/sunxi-mmc.c
+++ b/drivers/mmc/host/sunxi-mmc.c
@@ -816,6 +816,20 @@ static void sunxi_mmc_request(struct mmc_host *mmc, struct
mmc_request *mrq)
}
}
+ /*
+ * TODO Support signal voltage switching
+ *
+ * Compared to Allwinner's kernel, recent updates in the mmc core
+ * mean this should be as easy as setting the flags in cmd_val and
+ * imask, and waiting for it to finish. However no boards support
+ * this so this cannot be tested. Block it for now.
+ */
+ if (cmd->opcode == SD_SWITCH_VOLTAGE) {
+ mrq->cmd->error = -EPERM;
+ mmc_request_done(mmc, mrq);
+ return;
+ }
+
if (cmd->opcode == MMC_GO_IDLE_STATE) {
cmd_val |= SDXC_SEND_INIT_SEQUENCE;
imask |= SDXC_COMMAND_DONE;
--
2.7.0.rc3
