[PATCH 3/3] ARM: dts: exynos5422-odroidxu3: Added UHS-I bus speed support

[Anand Moon]

Hi Krzysztof,

On 13 October 2015 at 05:44, Krzysztof Kozlowski
<k.kozlowski at samsung.com> wrote:
> On 13.10.2015 00:32, Anand Moon wrote:
>> Hi Krzysztof,
>>
>> On 12 October 2015 at 11:14, Krzysztof Kozlowski
>> <k.kozlowski at samsung.com> wrote:
>>> On 12.10.2015 00:46, Anand Moon wrote:
>>>> Added support for UHS-I bus speed 50MB/s (SDR50, DDR50) 104MB/s (SDR104)
>>>
>>> This description is not entirely correct. The MMC driver already
>>> supports these UHS speeds (you did not any code) so you rather enabled
>>> it (description of bindings says "is supported").
>>>
>>> You mentioned DDR50 but I don't see respective property below.
>>>
>>> How do you know that these modes are really supported? I don't know. Can
>>> you convince me?
>>
>> Setting this DDR50 capability give me this error. That's the reason to
>> drop this capability.
>
> But you mentioned it in commit message! "Added support for UHS-I ...
> (DDR50)"
>
> In the same time dropping DDR50 is not an sufficient proof that "SDR50
> and SDR104 are really supported".
>

These changes are related to the microSD card capabilities.
So SDR50 have better frequency over DDR50. On the same Sandisk card.

When the card select the capability for DDR50
---------------------------------------------------
[    4.001477] mmc_host mmc1: Bus speed (slot 0) = 50000000Hz (slot
req 50000000Hz, actual 50000000HZ div = 0)
[    4.001604] mmc1: new ultra high speed DDR50 SDHC card at address aaaa
[    4.004505] mmcblk0: mmc1:aaaa SL32G 29.7 GiB
[    4.009179] mmcblk0: error -110 sending status command, retrying
[    4.009271] mmcblk0: error -115 sending stop command, original cmd
response 0x900, card status 0x900
[    4.009275] mmcblk0: error -84 transferring data, sector 0, nr 8,
cmd response 0x900, card status 0x0
[    4.025563] mmc_host mmc1: Bus speed (slot 0) = 50000000Hz (slot
req 400000Hz, actual 396825HZ div = 63)
[    4.067770] Console: switching to colour frame buffer device 274x77
[    4.098782] mmc_host mmc1: Bus speed (slot 0) = 50000000Hz (slot
req 50000000Hz, actual 50000000HZ div = 0)
[    4.099692] mmc1: tried to reset card
[    4.101332]  mmcblk0: p1 p2


When the card select the capability for SDR50
---------------------------------------------------------------------------------
[ 2.439806] mmc_host mmc1: Bus speed (slot 0) = 100000000Hz (slot req
100000000Hz, actual 100000000HZ div = 0)
[ 2.449729] mmc1: new ultra high speed SDR50 SDHC card at address aaaa
[ 2.455984] mmcblk0: mmc1:aaaa SL32G 29.7 GiB
[ 2.461743] mmcblk0: p1 p2

Which will relate to better read/write speed.

-Anand Moon


> Best regards,
> Krzysztof
>