mmc: dw_mmc: introduce timer for broken command transfer over scheme

Per the databook of designware mmc controller 2.70a, table 3-2, cmd
done interrupt should be fired as soon as the the cmd is sent via
cmd line. And the response timeout interrupt should be generated
unconditioinally as well if the controller doesn't receive the resp.
However that doesn't seem to meet the fact of rockchip specified Soc
platforms using dwmmc. We have continuously found the the cmd done or
response timeout interrupt missed somehow which took us a long time to
understand what was happening. Finally we narrow down the root to
the reconstruction of sample circuit for dwmmc IP introduced by
rockchip and the buggy design sweeps over all the existing rockchip
Socs using dwmmc disastrously.

It seems no way to work around this bug without the proper break-out
mechanism so that we seek for a parallel pair the same as the handling
for missing data response timeout, namely dto timer. Adding this cto
timer seems easily to handle this bug but it's hard to restrict the code
under the rockchip specified context. So after merging this patch, it
sets up the cto timer for all the platforms using dwmmc IP which isn't
ideal but at least we don't advertise new quirk here. Fortunately, no
obvious performance regression was found by test and the pre-existing
similar catch-all timer for sdhci has proved it's an acceptant way to
make the code as robust as possible.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=196321
Signed-off-by: Addy Ke <addy.ke@rock-chips.com>
Signed-off-by: Ziyuan Xu <xzy.xu@rock-chips.com>
[shawn.lin: rewrite the code and the commit msg throughout]
Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/drivers/mmc/host/dw_mmc.h b/drivers/mmc/host/dw_mmc.h
index 5403758bf621..34474ad731aa 100644
--- a/drivers/mmc/host/dw_mmc.h
+++ b/drivers/mmc/host/dw_mmc.h
@@ -126,6 +126,7 @@ struct dw_mci_dma_slave {
  * @irq: The irq value to be passed to request_irq.
  * @sdio_id0: Number of slot0 in the SDIO interrupt registers.
  * @cmd11_timer: Timer for SD3.0 voltage switch over scheme.
+ * @cto_timer: Timer for broken command transfer over scheme.
  * @dto_timer: Timer for broken data transfer over scheme.
  *
  * Locking
@@ -232,6 +233,7 @@ struct dw_mci {
 	int			sdio_id0;
 
 	struct timer_list       cmd11_timer;
+	struct timer_list       cto_timer;
 	struct timer_list       dto_timer;
 };