Re: [PATCH v2] mmc: support BKOPS feature for eMMC

[Jaehoon Chung <jh80.chung@samsung.com>]

Hi Kostya

On 11/28/2011 06:39 PM, Konstantin Dorfman wrote:

> Hello Jaehoon, Per
> 
> I have experimented with eMMC v4.41 card and BKOPS feature and want to add
> info on EXT_CSD_BKOPS_EN[163] field. See below.
> 
>> Hi Per
>>
>>>>>>>>
>>>>>>>>        if (card->ext_csd.rev >= 5) {
>>>>>>>> +               /* check whether the eMMC card support BKOPS */
>>>>>>>> +               if (ext_csd[EXT_CSD_BKOPS_SUPPORT] & 0x1) {
>>>>>>>> +                       card->ext_csd.bkops = 1;
>>>>>>>> +                       card->ext_csd.bkops_en = 1;
>>>>>>> What if the card has not enabled bkops? This bit could be unset.
>>>>>>> card->ext_csd.bkops_en = ext_csd[EXT_CSD_BKOPS_EN];
>>>>>> When card is supported the bkops, bkops_en bit is set by default...
>>>>>>
>>>>> How do you know if the bkops_en is really enabled in th ext_csd?
>>>>> It could be unset in the ext_csd, right?
>>>>
>>>> In emmc4.5 spec, if card is supported the bkops, bkops_en is set by
>>>> default.
>>> If bkops_en is set by default it should be in the the ext_csd too,
>>> right?
>>> It should be safer to trust the value of ext_csd[EXT_CSD_BKOPS_EN] in
>>> this case I think.
>>
>> If we want to ensure whether bkops_en bit is set or not, your approach is
>> right.
>>
>> Best Regards,
>> Jaehoon Chung
> 
> First of all protocol state:
> ------------------------------
> 7.4.57 BKOPS_EN [163]
> This field allows the _host_ to indicate to the device if it is expected
> to periodically manually start background operations by writing to the
> BKOPS_START field.
> 
> ...In order for the device to know if host is going to periodically start
> background operations, host shall set bit 0 of BKOPS_EN (EXT_CSD byte
> [163]) to indicate that it is going to write to BKOPS_START periodically.
> The device may then delay some of its maintenance operations to when host
> writes to BKOPS_START.
> ------------------------------
> 
> My card supports BKOPS (by reading Bit 0 of BKOPS_SUPPORT (EXT_CSD byte
> [502]), but BKOPS_EN[163] is not set. So I suppose, original code to set
> BKOPS_EN[163] is needed, otherwise card will never delay its maintenance
> operations.


Ok...i will add the code for setting BKOPS_EN bit in patch-v4.
Thanks,
Jaehoon Chung