Re: [PATCH v2 1/2] mmc: Add support for marking hpi as broken through devicetree

[Olliver Schinagl <oliver+list-dxLnbx3+1qmEVqv0pETR8A@public.gmane.org>]

Hey Hans,

On 08-10-15 14:13, Olliver Schinagl wrote:
> Hey Hans,
>
>
> On 08-10-15 10:43, Hans de Goede wrote:
>> Hi,
>>
>> On 10/07/2015 09:43 AM, Olliver Schinagl wrote:
>>> Hey Hans,
>>>
>>> On 01-04-15 17:26, Hans de Goede wrote:
>>>> The eMMC on a tablet I've will stop working / communicating as soon as
>>>> the kernel executes:
>>>>
>>>>         mmc_switch(card, EXT_CSD_CMD_SET_NORMAL,
>>>>                   EXT_CSD_HPI_MGMT, 1,
>>>>                   card->ext_csd.generic_cmd6_time);
>>>>
>>>> There seems to be no way to reliable identify eMMC-s which have a 
>>>> broken
>>>> hpi implementation, but at least for eMMC's which are soldered onto 
>>>> a board
>>>> we can work around this by specifying that hpi is broken in 
>>>> devicetree.
>>> We've been talking about this a little off-list, and I was just 
>>> triggered again by this so I'm following up on it again.
>>>
>>> The same issue bit me in the ass on a Micron 'industrial' grade eMMC 
>>> (MTFC4GACAANA) and luckily you found this back then to help me.
>>>
>>> As we discussed, this may very well be a limitation of the mmc 
>>> controller, rather then the MMC chip. While we only have a sample 
>>> size of 2 on 2 different socs (with likely the same mmc IP) 
>>> (A13/A20) I found in the JEDEC spec in the appendix on changes from 
>>> 4.4 to 4.41:
>>> Introduce of High Priority Interrupt mechanism, HPI background and 
>>> one of possible solutions.
>>>
>>> Which leaves me to believe, that HPI was added to eMMC in version 
>>> 4.41 and was not available before. Both the A13 and A20 user manuals 
>>> state that the MMC controller in these socs is only version 4.3.
>>>
>>> Obviously I know far to little as to what does and what does not 
>>> work with an MMC-host, since it's just a simple data-bus, but I 
>>> would not be surprised if these things are somewhere somewhat 
>>> related, so hopefully someone on this list can give their opinion on 
>>> this.
>>>
>>> I already checked the core/mmc.c where the version is read from the 
>>> mmc controller to see if we can trigger on this based on version, 
>>> however it seems only the major version number is stored here [0]?
>>>
>>> So in my opinion, it is quite likely that this setting be moved up 
>>> to the mmc-core level, for the SoC, rather then the card itself?
>>
>> Yes I was talking to Tsvetan from Olimex and he says they have seen 
>> the problem with yet
>> another emmc, so this indeed seems to be a sunxi SoC specific 
>> problem, and we just need to
>> disable hpi on all sunxi SoC's.
>>
>> Do you have time to look into doing a kernel patch for this ?
>>
>> I'm thinking adding a host-cap called MMC_CAP_BROKEN_HPI and adding
>> support for that to drivers/mmc/core/host.c: mmc_of_parse() and
>> extending the current card check for broken-hpi to also check
>> host->caps
>>
>> And then we need to decide whether to just hard set that cap
>> in drivers/mmc/host/sunxi_mmc.c or if we are going to add it
>> to our dtsi files. I think we should probably just hard-code
>> it in drivers/mmc/host/sunxi_mmc.c.
> Yeah I'll see if I can look into that.
>
> I was also looking if we really cannot detect older MMC versions, and 
> I think we can somewhat. I haven't figured out the details yet though.
>
> The EXT_CSD_REV field does yield a version number matching the various 
> 4 sub-versions, so for now I'm thinking of simply disabeling HPI for 
> anything before 4.41 (unless maybe overriden). Since before 4.41 it 
> shouldn't have been supported. Maybe add an override that allows use 
> of HPI? but then we have the whole backwards compatibility thing.
>
> [0] http://lxr.free-electrons.com/source/drivers/mmc/core/mmc.c#L368

I re-read what you said and looked at the files and think your idea is 
probably best, since there is no version information (in sunxi_mmc.c for 
example) anyway). So there is versioning information on the card level 
and the mmc core level, but not in the host level.

The quick fix, is to use MMC_CAP_BROKEN_HPI
The better fix that would feel better/proper to use MMC_CAP_HPI instead, 
to indicate that a chipset actually can do HPI, since nothing says our 
chipset should do HPI (v4.3 that we have doesn't support it at all).

I'm debating if it would be usefull to have a version field in the mmc 
host struct, which would set some capabilities by default based on the 
version level, but I don't think we have that many capabilities right 
now anyway do we?

P.S. you want to keep the broken-hpi flag (on a card level?) for 
backwards compatibility with older dts files? Or move it to the host 
level so that the MMC_CAP_BROKEN_HPI field can be overriden via the dts? 
So sunxi-mmc.c sets MMC_CAP_BROKEN_HPI, a user could still set 
broken-hpi to false to indicate the HPI is actually working for him?

Olliver
>>
>> Regards,
>>
>> Hans
>>
>>
>>
>>
>>
>>
>>>
>>> [0] http://lxr.free-electrons.com/source/drivers/mmc/core/mmc.c#L148
>>>>
>>>> Signed-off-by: Hans de Goede <hdegoede-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
>>>> ---
>>>> Changes in v2:
>>>> -Fix of_node leakage
>>>> ---
>>>>   Documentation/devicetree/bindings/mmc/mmc-card.txt | 31 
>>>> ++++++++++++++++++++++
>>>>   drivers/mmc/core/mmc.c                             | 10 ++++++-
>>>>   2 files changed, 40 insertions(+), 1 deletion(-)
>>>>   create mode 100644 
>>>> Documentation/devicetree/bindings/mmc/mmc-card.txt
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/mmc/mmc-card.txt 
>>>> b/Documentation/devicetree/bindings/mmc/mmc-card.txt
>>>> new file mode 100644
>>>> index 0000000..a70fcd6
>>>> --- /dev/null
>>>> +++ b/Documentation/devicetree/bindings/mmc/mmc-card.txt
>>>> @@ -0,0 +1,31 @@
>>>> +mmc-card / eMMC bindings
>>>> +------------------------
>>>> +
>>>> +This documents describes the devicetree bindings for a mmc-host 
>>>> controller
>>>> +child node describing a mmc-card / an eMMC, see "Use of Function 
>>>> subnodes"
>>>> +in mmc.txt
>>>> +
>>>> +Required properties:
>>>> +-compatible : Must be "mmc-card"
>>>> +-reg        : Must be <0>
>>>> +
>>>> +Optional properties:
>>>> +-broken-hpi : Use this to indicate that the mmc-card has a broken hpi
>>>> +              implementation, and that hpi should not be used
>>>> +
>>>> +Example:
>>>> +
>>>> +&mmc2 {
>>>> +    pinctrl-names = "default";
>>>> +    pinctrl-0 = <&mmc2_pins_a>;
>>>> +    vmmc-supply = <&reg_vcc3v3>;
>>>> +    bus-width = <8>;
>>>> +    non-removable;
>>>> +    status = "okay";
>>>> +
>>>> +    mmccard: mmccard@0 {
>>>> +        reg = <0>;
>>>> +        compatible = "mmc-card";
>>>> +        broken-hpi;
>>>> +    };
>>>> +};
>>>> diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
>>>> index 1d41e85..c84131e 100644
>>>> --- a/drivers/mmc/core/mmc.c
>>>> +++ b/drivers/mmc/core/mmc.c
>>>> @@ -11,6 +11,7 @@
>>>>    */
>>>>   #include <linux/err.h>
>>>> +#include <linux/of.h>
>>>>   #include <linux/slab.h>
>>>>   #include <linux/stat.h>
>>>>   #include <linux/pm_runtime.h>
>>>> @@ -336,6 +337,8 @@ static int mmc_decode_ext_csd(struct mmc_card 
>>>> *card, u8 *ext_csd)
>>>>   {
>>>>       int err = 0, idx;
>>>>       unsigned int part_size;
>>>> +    struct device_node *np;
>>>> +    bool broken_hpi = false;
>>>>       /* Version is coded in the CSD_STRUCTURE byte in the EXT_CSD 
>>>> register */
>>>>       card->ext_csd.raw_ext_csd_structure = 
>>>> ext_csd[EXT_CSD_STRUCTURE];
>>>> @@ -349,6 +352,11 @@ static int mmc_decode_ext_csd(struct mmc_card 
>>>> *card, u8 *ext_csd)
>>>>           }
>>>>       }
>>>> +    np = mmc_of_find_child_device(card->host, 0);
>>>> +    if (np && of_device_is_compatible(np, "mmc-card"))
>>>> +        broken_hpi = of_property_read_bool(np, "broken-hpi");
>>>> +    of_node_put(np);
>>>> +
>>>>       /*
>>>>        * The EXT_CSD format is meant to be forward compatible. As long
>>>>        * as CSD_STRUCTURE does not change, all values for EXT_CSD_REV
>>>> @@ -494,7 +502,7 @@ static int mmc_decode_ext_csd(struct mmc_card 
>>>> *card, u8 *ext_csd)
>>>>           }
>>>>           /* check whether the eMMC card supports HPI */
>>>> -        if (ext_csd[EXT_CSD_HPI_FEATURES] & 0x1) {
>>>> +        if (!broken_hpi && (ext_csd[EXT_CSD_HPI_FEATURES] & 0x1)) {
>>>>               card->ext_csd.hpi = 1;
>>>>               if (ext_csd[EXT_CSD_HPI_FEATURES] & 0x2)
>>>>                   card->ext_csd.hpi_cmd = MMC_STOP_TRANSMISSION;
>>>
>>
>