On Mon, Dec 5, 2016 at 5:24 PM, Caleb Crome <caleb@xxxxxxxxx> wrote:
> On Mon, Dec 5, 2016 at 4:46 PM, Fabio Estevam <festevam@xxxxxxxxx> wrote:
>> Hi Caleb,
>>
>> On Mon, Dec 5, 2016 at 10:36 PM, Caleb Crome <caleb@xxxxxxxxx> wrote:
>>> Hello,
>>> We have a board here where there is a signal integrity problem on the MMC
>>> bus. It works fine at 25MHz, but does not work in higher speed modes.
>>>
>>> Is there an easy way to disable all the high speed modes? Perhaps from the
>>> device tree?
>>>
>>> I tried searching the archives, but gmane seems to be not working.
>>>
>>> I'm using a stock 4.8.11 kernel.
>>> Host processor is i.MX6
>>
>> Would max-frequency = <25000000>; do the trick?
>>
>> Please take a look at Documentation/devicetree/bindings/mmc/mmc.txt .
>
> Hi Fabio,
> Thanks for the quick feedback -- I was momentarily hopeful...
> Unfortunatley, that doesn't seem to work.
>
> I have set (using a solid-run hummingboard uSOM):
> &usdhc2 {
> pinctrl-names = "default";
> pinctrl-0 = <
> &pinctrl_hummingboard_usdhc2_aux
> &pinctrl_hummingboard_usdhc2
> >;
> vmmc-supply = <®_3p3v>;
> cd-gpios = <&gpio1 4 GPIO_ACTIVE_LOW>;
> max-frequency = <25000000>;
> status = "okay";
> };
>
> and just for good measure I set:
> &usdhc1 {
> max-frequency = <25000000>;
> };
> &usdhc3 {
> max-frequency = <25000000>;
> };
> &usdhc4 {
> max-frequency = <25000000>;
> };
> (though I'm pretty sure it's using SD2).
>
> And it not only attempts to clock at 50MHz, but also at 200 MHz -- way
> beyond what the board can support.
>
> Basically, it doesn't seem to be heeding the max-frequency DT setting at all.
>
> I did in fact verify that the max-frequency value was read at
> http://lxr.free-electrons.com/source/drivers/mmc/core/host.c#L216, and
> the host->f_max frequency was set to 25000000, but that f_max was
> ignored it seems.
>
Okay, I take it back -- sort of.
The f_max is not ignored -- if I set 5MHz, the clock is *usually* 5MHz.
However, I have a trigger set with my scope, and it actually does
switch to 200MHz mode momentarily. I don't know whether or not this
is the cause of my problems.
Currently, my problem is that I get hard reboot just as the following
happens: (This is a different problem from before I switch
max-frequency).
[ 5.293356] random: fast init done
[ 5.298871] ALSA device list:
[ 5.301973] #0: On-board SPDIF
[ 5.318480] EXT4-fs (mmcblk0p2): mounting ext3 file system using
the ext4 subsystem
[ 5.350791] mmc1: new SDIO card at address 0001
[ 5.379811] EXT4-fs (mmcblk0p2): mounted filesystem with ordered
data mode. Opts: (null)
[ 5.388118] VFS: Mounted root (ext3 filesystem) on device 179:2.
[ 5.411692] devtmpfs: mounted
U-Boot SPL 2013.10-rc4 (Dec 05 2016 - 14:09:51)
Boot Device: SD1
spl: error reading image u-boot.img, err - -1
Load image from RAW...
Here is an image of the scope capture showing the sd_clk transition
from 5MHz to 200MHz in the middle of booting.
https://drive.google.com/open?id=0BxzZmuc2tSowTzRHUms5RW9mUkE
Thanks again,
-Caleb
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