Re: [PATCH v3] mmc: support BKOPS feature for eMMC

[Adrian Hunter <adrian.hunter@intel.com>]

On 17/11/11 02:50, Jaehoon Chung wrote:
> Enable eMMC background operations (BKOPS) feature.
> 
> If URGENT_BKOPS is set after a response, note that BKOPS
> are required. After all I/O requests are finished, run
> BKOPS if required. Should read/write operations be requested
> during BKOPS, first issue HPI to interrupt the ongoing BKOPS
> and then service the request.
> 
> If you want to enable this feature, set MMC_CAP2_BKOPS.
> 
> Future considerations
>  * Check BKOPS_LEVEL=1 and start BKOPS in a preventive manner.
>  * Interrupt ongoing BKOPS before powering off the card.
> 
> Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
> Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
> CC: Hanumath Prasad <hanumath.prasad@stericsson.com>
> ---
> Changelog V3:
> 	- move the bkops setting's location in mmc_blk_issue_rw_rq
> 	- modify condition checking
> 	- bkops_en is assigned ext_csd[EXT_CSD_BKOPS_EN] instead of "1"
> 	- remove the unused code
> 	- change pr_debug instead of pr_warn in mmc_send_hpi_cmd
> 	- Add the Future consideration suggested by Per
> 	
> Changelog V2:
> 	- Use EXCEPTION_STATUS instead of URGENT_BKOPS
> 	- Add function to check Exception_status(for eMMC4.5)
> 	- remove unnecessary code.
> 

The main problem with bkops is:

	If the status is at level 3 ("critical"), some operations
	may extend beyond their original timeouts due to maintenance
	operations which cannot be delayed anymore.

This means:

	1. at level 3 either bkops are run or the timeout of the next
	(data?) operation is extended

	2. at level 3 either the bkops must not be interrupted or the
	level must be rechecked after interruption and bkops run again
	if the level is still 3