[PATCH 2/3] mmc: sunxi: Fix DDR MMC timings for A80

On Mon, May 30, 2016 at 8:59 PM, Chen-Yu Tsai [off-list ref] wrote:

On Mon, May 30, 2016 at 7:34 PM, Hans de Goede [off-list ref] wrote:

quoted

Hi,

On 29-05-16 09:04, Chen-Yu Tsai wrote:

quoted

The MMC clock timings were incorrectly calculated, when the conversion
from delay value to delay phase was done.

The 50M DDR and 50M DDR 8bit timings are off, and make eMMC DDR
unusable. Unfortunately it seems different controllers on the same SoC
have different timings. The new settings are taken from mmc2, which is
commonly used with eMMC.

Hmm, I'm not really all that familiar with mmc, but can't an external
sdcard connected to mmc0 use DDR too ? Assuming the answer is yes, then
we really need to update the driver to use the right per controller
timings.

I would very much like that to happen. However, SD card UHS-1 DDR modes
require 1.8V signaling, which is unavailable on _all_ sunxi boards.
This seems like a limit of most of the SoCs not having a separate IO
voltage rail for mmc pins.

Until then, I wouldn't worry that much.

P.S. I also tried the settings from mmc0 in Allwinner sources. They gave
horrible results ( < 5 MB/s read ) on my CC-A80, while my Optimus wasn't
really affected. I wonder if there's some kind of auto-retry mechanism
in the MMC controller, or driver?

ChenYu

quoted

quoted

The settings for the slower timing modes seem to work despite being
wrong, so leave them be.

If you're sure the timings are wrong, please fix them. Sometimes wrong
timings do seem to work, but lead to unreliable communication, or turn
out to work on some boards and not on others due to routing differences.

Unfortunately I did try putting in the correct numbers for them, and my
eMMC then failed to probe. It seems the core switches up from 400kHz to
50MHz then to 50MHz DDR, and it fails somewhere in there, maybe at 50MHz.

I'm not sure if we need to add DT bindings to specify different delays
for different controllers, though. Seems like we'll never actually use
it.

Hope this answers your questions.

Regards
ChenYu

quoted

Thanks & Regards,

Hans

quoted

Signed-off-by: Chen-Yu Tsai <redacted>
---
 drivers/mmc/host/sunxi-mmc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/mmc/host/sunxi-mmc.c b/drivers/mmc/host/sunxi-mmc.c
index 7fc8b7aa83f0..5873dc344ab2 100644
--- a/drivers/mmc/host/sunxi-mmc.c
+++ b/drivers/mmc/host/sunxi-mmc.c

@@ -970,8 +970,8 @@ static const struct sunxi_mmc_clk_delay

sun9i_mmc_clk_delays[] = {
        [SDXC_CLK_400K]         = { .output = 180, .sample = 180 },
        [SDXC_CLK_25M]          = { .output = 180, .sample =  75 },
        [SDXC_CLK_50M]          = { .output = 150, .sample = 120 },
-       [SDXC_CLK_50M_DDR]      = { .output =  90, .sample = 120 },
-       [SDXC_CLK_50M_DDR_8BIT] = { .output =  90, .sample = 120 },
+       [SDXC_CLK_50M_DDR]      = { .output =  54, .sample =  36 },
+       [SDXC_CLK_50M_DDR_8BIT] = { .output =  72, .sample =  72 },
 };

 static int sunxi_mmc_resource_request(struct sunxi_mmc_host *host,