On 30 January 2017 at 10:40, Adrian Hunter [off-list ref] wrote:

On 30/01/17 11:10, Ulf Hansson wrote:

quoted

On 28 January 2017 at 09:16, Adrian Hunter [off-list ref] wrote:

quoted

On 27/01/2017 5:12 p.m., Ulf Hansson wrote:

quoted

On 26 January 2017 at 13:39, Adrian Hunter [off-list ref]
wrote:

quoted

On 26/01/17 12:50, Ulf Hansson wrote:

quoted

On 11 January 2017 at 18:19, Gregory CLEMENT
[off-list ref] wrote:

quoted

+                       priv->init_card_type = MMC_TYPE_MMC;
+                       mmc->caps |= MMC_CAP_NONREMOVABLE;
+
+                       /*
+                        * Force to clear BUS_TEST to
+                        * skip bus_test_pre and bus_test_post
+                        */
+                       mmc->caps &= ~MMC_CAP_BUS_WIDTH_TEST;
+                       mmc->caps2 |= MMC_CAP2_HC_ERASE_SZ |

This cap is a bit strange. It was added several years ago by Adrian
Hunter, but I am wondering about the reason to why it's needed.

MMC_CAP2_HC_ERASE_SZ relates to EXT-CSD ERASE_GROUP_DEF.

I think it was added to enable people to choose whether they wanted a
large
or small erase granularity.  That probably doesn't matter if the card
supports TRIM.

Huh, the erase/trim/discard code in the mmc core is really hairy. :-)

In mmc_calc_max_discard() the following code/comment exists:

/*
 * Without erase_group_def set, MMC erase timeout depends on clock
 * frequence which can change.  In that case, the best choice is
 * just the preferred erase size.
 */
if (mmc_card_mmc(card) && !(card->ext_csd.erase_group_def & 1))
     return card->pref_erase;


This makes me wonder.

So, when we haven't enabled the high capacity erase groups in the
EXT_CSD register (ext_csd.erase_group_def), we will use the pref_erase
size.

In the other case, as when having MMC_CAP2_HC_ERASE_SZ set (which will
set ext_csd.erase_group_def),  we will instead  do some calculations
to find out the max discards.

Are you saying that these calculations doesn't matter much - or are
you saying that we always want to do them?

No, I was saying that if you have TRIM then TRIM is preferred to ERASE so
the erase group size does not come into play when discarding, since ERASE
granularity is erase groups whereas TRIM granularity is sectors.

Right. Thanks for clarifying.

quoted

However ERASE_GROUP_DEF also affects the size of write protect groups.

In either case.

What do you think of removing MMC_CAP2_HC_ERASE_SZ? I don't like these
kind of soft polices, it's better if we can decide on a common
behaviour - whatever that is.

Changing the value of ERASE_GROUP_DEF could be a problem, for example the
spec. says:

"Similarly if the host set ERASE_GROUP_DEF bit for a device that the default
write protect was already set in some of the area in the previous power
cycle, then the device may show unknown behavior when host issue write
or erase commands to the device. In application, it is mandatory for host to
use same ERASE GROUP DEF value to the device all the time."

Whether or not there is anyone that would actually be affected is hard to know.

Okay. I am going to submit a patch that just removes the behaviour for
MMC_CAP2_HC_ERASE_SZ and the cap itself.

The cap isn't particular widely used anyway. Let's see what people think of it.

Thanks a lot for you input!

Kind regards
Uffe