Re: [linux-sunxi] [PATCH 2/2] mmc: sunxi: fix new timings mode on A64 EMMC (MMC2) controller

From: Icenowy Zheng
Date: Sat Aug 05 2017 - 23:25:29 EST

ä 2017å8æ6æ GMT+08:00 äå10:39:54, Chen-Yu Tsai <wens@xxxxxxxx> åå:
>On Sat, Aug 05, 2017 at 05:35:55AM +0800, Icenowy Zheng wrote:
>> The configuration struct of A64 EMMC(MMC2) compatible used to
>> have the needs_new_timings variable missing, which lead to NULL
>> pointer dereference now when trying to set up the old timings mode,
>> the old timings mode doesn't exist at all on A64.
>I'm not familiar with the A64's eMMC controller. The datasheet says
>it does not have the timing switch register. It does not say whether
>it is always in the old or new timing mode. "needs_new_timings"
>probably meant that the switch has to be set.

As I know, it supports DDR mode, but the CCU has no clk delays.
So it should be the new timings mode.

>This fix doesn't really fix the underlying issue, which is the check
>for clk_delays was incorrectly replaced. sun4i/sun5i is also broken.
>Could you try this patch instead:
>From 23b841a11294cb6a0cf1e146616b068f60c2ec7d Mon Sep 17 00:00:00 2001
>From: Chen-Yu Tsai <wens@xxxxxxxx>
>Date: Sun, 6 Aug 2017 10:24:47 +0800
>Subject: [PATCH] mmc: sunxi: Fix NULL pointer reference on clk_delays
>Some SoCs do not support clk delays for MMC in the clock control unit.
>These include the old controllers in A10/A10s/A13/R8, and the new eMMC
>controller in A64. The config structure for these controllers do not
>specify clk_delays, but the check for this was replaced in commit
>b0600daebf31 ("mmc: sunxi: Support controllers that can use both old
>and new timings").
>This patch adds back the check for clk_delays, and also adds comments
>for both checks in sunxi_mmc_clk_set_phase().
>Fixes: b0600daebf31 ("mmc: sunxi: Support controllers that can use
> both old and new timings")
>Signed-off-by: Chen-Yu Tsai <wens@xxxxxxxx>
> drivers/mmc/host/sunxi-mmc.c | 5 +++++
> 1 file changed, 5 insertions(+)
>diff --git a/drivers/mmc/host/sunxi-mmc.c
>index 3777517982dd..020547e5fa45 100644
>--- a/drivers/mmc/host/sunxi-mmc.c
>+++ b/drivers/mmc/host/sunxi-mmc.c
>@@ -722,9 +722,14 @@ static int sunxi_mmc_clk_set_phase(struct
>sunxi_mmc_host *host,
> {
> int index;
>+ /* No need to set clk controller delays under new timings */
> if (host->use_new_timings)
> return 0;
>+ /* Some old controllers don't support delays */
>+ if (!host->cfg->clk_delays)
>+ return 0;
> /* determine delays */
> if (rate <= 400000) {
> index = SDXC_CLK_400K;