On 8 August 2017 at 13:44, Shawn Lin <shawn.lin@xxxxxxxxxxxxxx> wrote: > Per SD specification version 4.10, section 4.3.4, it says "pre-erased > (ACMD23) will make a following Multiple Block Write operation faster > compared to the same operation without preceding ACMD23". ACMD23 is > mandatory for all sd cards and the spec also says "Command STOP_TRAN > (CMD12) shall be used to stop the transmission in Write Multiple Block > whether or not the preerase (ACMD23) feature is used." > > However current code only check to see if CMD23 is available. If not, > it would fallback to open-ending mode. So this catch-all RFC patch > is trying to activate ACMD23 support for SD cards when doing multiple > write. > > I have been testing it for while with all different kinds of SD cards > . But what makes me hesitate to submit a formal patch is that > > (1) > If the SD card does support CMD23 as well as the host, then we don't > use ACMD23 as I don't see *obvious* write performance boost for > ACMD23 vs CMD23 when doing multiple write for most of the cards, > although some of them do improve a little. So this makes me though that > the behaviour of dealing with ACMD23 or CMD23 depends on the firmware > designed. Just so I get this right... If the card supports CMD23, then you mean we are fine with the current code as is? However, if the card don't support CMD23, but ACMD23, $subject patch *may* offer an improvement. Right? That leads to yet another question. Are there many SD cards that don't support CMD23 but ACMD23? > > (2) > If enabling ACMD23 for SD cards, I did see a interesting thing that > some of the cards fail to return to tran state even when the host > fires CMD12 which meets the requirement of spec. When debugging, I saw > these buggy cards was still in recv state and never changed. So I did > some hack to trace the card status and fire CMD12 again if possible. > > (3) > I test all of my SD cards at hand, and try to figure out if we benefit > from ACMD23 vs open-ending multiple write. When using ACMD23, we fire > extra ACMD23 which would lower the write performance theoretically, > although I also didn't see any *obviuos* thoughput drop. The only > visible benefit is that pre-erased multiple write is more 'stable' > than open-ending multiple write, just as the same reason for why we > prefer to use CMD23 instead of open-ending mode. Overall, I wouldn't have any issues of enabling ACMD23 for SD cards - if only it could be justified as providing an improved behavior. I guess we will need more peoples opinion and help in test to understand better. [...] Kind regards Uffe -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
