mmc: mmci: Make busy complete state machine explicit

This refactors the ->busy_complete() callback currently
only used by Ux500 and STM32 to handle busy detection on
hardware where one and the same IRQ is fired whether we get
a start or an end signal on busy detect.

The code is currently using the cached status from the
command IRQ in ->busy_status as a state to select what to
do next: if this state is non-zero we are waiting for
IRQs and if it is zero we treat the state as the starting
point for a busy detect wait cycle.

Make this explicit by creating a state machine where the
->busy_complete callback moves between three states.

The Ux500 busy detect code currently assumes this order:
we enable the busy detect IRQ, get a busy start IRQ, then a
busy end IRQ, and then we clear and mask this IRQ and
proceed.

We insert debug prints for unexpected states.

This works as before on most cards, however on a
problematic card that is not working with busy detect, and
which I have been debugging, the following happens a lot:

[    3.380554] mmci-pl18x 80005000.mmc: no busy signalling in time
[    3.387420] mmci-pl18x 80005000.mmc: no busy signalling in time
[    3.394561] mmci-pl18x 80005000.mmc: lost busy status
     when waiting for busy start IRQ

This probably means that the busy detect start IRQ has
already occurred when we start executing the
->busy_complete() callbacks, and the busy detect end IRQ
is counted as the start IRQ, and this is what is causing
the card to not be detected properly.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20230405-pl180-busydetect-fix-v7-5-69a7164f2a61@linaro.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

1 files changed, 14 insertions, 0 deletions

diff --git a/drivers/mmc/host/mmci.h b/drivers/mmc/host/mmci.h
index e1a9b96a3396..12a7bbd3ce26 100644
--- a/drivers/mmc/host/mmci.h
+++ b/drivers/mmc/host/mmci.h
@@ -262,6 +262,19 @@ struct dma_chan;
 struct mmci_host;
 
 /**
+ * enum mmci_busy_state - enumerate the busy detect wait states
+ *
+ * This is used for the state machine waiting for different busy detect
+ * interrupts on hardware that fire a single IRQ for start and end of
+ * the busy detect phase on DAT0.
+ */
+enum mmci_busy_state {
+	MMCI_BUSY_WAITING_FOR_START_IRQ,
+	MMCI_BUSY_WAITING_FOR_END_IRQ,
+	MMCI_BUSY_DONE,
+};
+
+/**
  * struct variant_data - MMCI variant-specific quirks
  * @clkreg: default value for MCICLOCK register
  * @clkreg_enable: enable value for MMCICLOCK register
@@ -409,6 +422,7 @@ struct mmci_host {
 	u32			clk_reg;
 	u32			clk_reg_add;
 	u32			datactrl_reg;
+	enum mmci_busy_state	busy_state;
 	u32			busy_status;
 	u32			mask1_reg;
 	u8			vqmmc_enabled:1;