On 5 June 2015 at 11:09, Lu Y.B. <yangbo.lu@xxxxxxxxxxxxx> wrote: >> On 5 June 2015 at 10:49, Lu Y.B. <yangbo.lu@xxxxxxxxxxxxx> wrote: >> >> On 5 June 2015 at 10:10, Lu Y.B. <yangbo.lu@xxxxxxxxxxxxx> wrote: >> >> >> >> On 2 June 2015 at 09:09, Yangbo Lu <yangbo.lu@xxxxxxxxxxxxx> >> wrote: >> >> >> >> > This quirk is used for controllers that can only support 1.8V >> >> >> >> > voltage but the peripheral hardware circuit has capability to >> >> >> >> > support 3.3V voltage. >> >> >> >> >> >> >> >> Which voltage are you referring to? The I/O voltage or the >> >> >> >> power to the card? VCC or VCCQ? >> >> >> >> >> >> >> >> Kind regards >> >> >> >> Uffe >> >> >> > >> >> >> > The voltage here means I/O voltage. >> >> >> > Although the controller only supports 1.8v, the hardware circuit >> >> >> > has a >> >> >> level translator for supporting 3.3v. >> >> >> >> >> >> Thanks for clarifying. >> >> > >> >> > Sorry, it should be power voltage... >> >> > This quirk is used to set capability register "Voltage Support 3.3V" >> >> bit since the controller self doesn’t support but circuit supports. >> >> > >> >> >> >> Okay. >> >> >> >> So then please tell me, exactly, how is the power being controlled >> >> when using this "hardware circuit"? >> >> >> >> This patchset only tries to change the content of the ocr_mask, but >> >> there is no logic added to support changing voltage levels by using >> >> the "external circuit". At least to my understanding. >> >> >> > >> > As I said, the controller only support 1.8v but we could use adapter >> card or add level translator on board directly to make sd *only* work on >> 3.3v power and 3.3v IO voltage. >> > Thanks. >> >> How does this level translator work? Doesn't it need to be controlled >> somehow? Do you have a datasheet you can share for it? >> > > I attached a adapter picture for you. > we would never control the power to change. > Although the io voltage could be control in design, we would never control it either. Always connect Vccb_SEL to GND. > Thanks. > This make it crystal clear to me, but I think you have some more homework to do. :-) This is a commonly used circuit to be able to boost the IO voltage levels from the SoC, towards the card. According to the SD spec, all cards needs to support the IO legacy voltage levels (2.7-3.6V). UHS-I SD cards, are also operate using 1.8V IO voltage, but the early initialization must be done using the legacy IO voltage level domain. So, I assume that when grounding Vccb_SEL, the IO voltage will be 2.9 V, which means you will always remain in legacy IO voltage level domain. That's fine, as long as you don't care about UHS cards. So, again this patchset really doesn't make sense. 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
