Hi, Wolfram, On 08.02.2024 02:56, Wolfram Sang wrote: > Hi Claudiu, > > I got more information about SMPCMP now. I had a misunderstanding there. > According to your patch description, you might have the same > misunderstanding? Let me quote again: > > === > RZ hardware manual are similar on this chapter), at the time of tuning, > data is captured by the previous and next TAPs and the result is stored in > the SMPCMP register (previous TAP in bits 22..16, next TAP in bits 7..0). > === > > It is not the previous and next TAP but the previous and next clock > cycle using the *same* TAP. And the bits in the register describe if > there was a mismatch in the data bits across these clock cycles. That's something new for me, it's not described in HW manual (or at least I haven't found it). > > So, we really want SMPCMP to be 0 because the data should be stable > across all three clock cycles of the same TAP. So, it means issues should be somewhere else on my setup. > >> As of my understanding the TAP where cmpngu = 0x0e and cmpngd=0x0e is not >> considered change point of the input data. For that to happen it would mean >> that cmpngu != cmpngd. > > I am not sure you can assume that cmpngu != cmpngd is always true for a > change point. I'd think it is likely often the case. But always? I am > not convinced. That's was my understanding from HW manual and since it fixed my issue I considered it valid at the point I wrote this statement. Maybe we need to understand this? > But I am convinced that if SMPCMP is 0, this is a good > TAP because it was stable over these clock cycles. > >> From this snapshot, datasheet and our discussions: >> >> i=0, cmpngu=00000000, cmpngd=00000000, smpcmp=00000000 >> i=1, cmpngu=00000000, cmpngd=00000000, smpcmp=00000000 >> i=2, cmpngu=0000000e, cmpngd=0000000e, smpcmp=000e000e >> i=3, cmpngu=00000000, cmpngd=00000000, smpcmp=00000000 >> *i=4, cmpngu=00000000, cmpngd=00000002, smpcmp=00000002* >> *i=5, cmpngu=00000000, cmpngd=000000ff, smpcmp=000001ff* >> *i=6, cmpngu=000000ff, cmpngd=00000000, smpcmp=01ff0000* >> i=7, cmpngu=00000000, cmpngd=00000000, smpcmp=00000000 >> i=8, cmpngu=00000000, cmpngd=00000000, smpcmp=00000000 >> i=9, cmpngu=00000000, cmpngd=00000000, smpcmp=00000000 >> i=10, cmpngu=00000000, cmpngd=00000000, smpcmp=00000000 >> i=11, cmpngu=00000000, cmpngd=00000000, smpcmp=00000000 >> *i=12, cmpngu=00000000, cmpngd=00000002, smpcmp=00000002* >> *i=13, cmpngu=00000000, cmpngd=000000ff, smpcmp=000001ff* >> *i=14, cmpngu=000000ff, cmpngd=00000000, smpcmp=01ff0000* >> i=15, cmpngu=00000000, cmpngd=00000000, smpcmp=00000000 >> >> I understand that TAP4,5,6 are change point of the input data and >> TAP8,0,1,2,3 are candidates for being selected, TAP 1,2 being the best >> (please correct me if I'm wrong). > > I agree that TAP4-6 are the change point. TAP2 could be a candidate. I > dunno why SMPCMP is non-zero at i == 2, maybe some glitch due to noise > on the board? Hm... it worth considering it... > > I do really wonder why probing failed, though? TAP1 sounds like a good > choice as well. I mean we consider SMPCMP only if all TAPs are good. So, > if probing fails, that means that SMPCMP was non-zero all the time? Yes, that was my finding as well on my setup which leads to this patch. If we're taking as example the snapshot I dropped here in a previous email, and do not consider this patch, code at [1] should clear bit for TAP2 in smpcmp mask because in the 1st round SMPCMP was not zero (but 0x000e000e) and in the 2nd round it was zero. [1] https://elixir.bootlin.com/linux/latest/source/drivers/mmc/host/renesas_sdhi_core.c#L629 > > That being said, our code to select the best TAP from SMPCMP is really > not considering the change point :( It just picks the first one where > SMPCMP is 0. Hm... I thought code at [2] selects the TAP in the middle (in the snapshot I pointed, TAP1). [1] https://elixir.bootlin.com/linux/latest/source/drivers/mmc/host/renesas_sdhi_core.c#L656 > We are not checking where the change point is and try to be > as far away as possible. > >> root@smarc-rzg3s:~# md5sum out test >> b053723af63801e665959d48cb7bd8e6 out >> b053723af63801e665959d48cb7bd8e6 test >> >> Do yo consider this enough? > > Yes, if done 100 times ;) This may take a while... > > I hope this mail was helpful? The tuning procedure it's better understand now. But I'm not sure in which direction should I dig further... :) Thank you for details and patience, Claudiu Beznea > > Thanks and happy hacking, > > Wolfram >
