On Mon, 26 Aug 2019 11:06:26 -0700 Philip Langdale <philipl@xxxxxxxxx> wrote: > > I started looking at how we might make a general change to ignore for > all > cards, and in the process, I saw that we already have a way to > differentiate > ocr_avail for different card types, and the sdhci driver uses this to > elide the low voltage range when dealing with SD cards. So I've made > the small change to have the rtsx drivers set ocr_avail_sd and skip > the low voltage > range support. This makes the cards work, as you'd expect. > > There's still a fair claim that the elidation logic should move into > the core, > so that all host controllers automatically benefit, but I think I > should leave > that to you. It's a core change and I don't pretend to understand all > the > considerations for all the various supported controllers. > > I've sent a new diff with the rtsx-specific fix. > More reading == more thoughts. So, I went through the simplified 6.0 spec more carefully and this is what I've extracted: * Low Voltage Signalling: The 1.8V I/O voltage we already support * Low Voltage Interface: A new 6.0 feature for setting VDD to 1.8V The LVI is documented in the "Low Voltage Interface Addendum" that is not included in the simplified spec. Why? Who knows. Do you have access to this by any chance? There are specific references in the simplified spec when discussing the OCR that make it pretty clear that bit 7 in the OCR indicates the card supports LVI and can be initialised in 1.8V mode if the LVI negotiation is followed. There is also a clear statement that an A2 card must support LVI. That means that the Sandisk card I'm looking at is 'correctly' setting bit 7 in OCR to indicate LVI support. And there's no "LV" logo because A2 implies LVI. It's deeply annoying that Low Voltage initialisation is done differently for SD vs MMC despite using the same mechanism to indicate support. Overall, this implies that until we can implement LVI negotiation, it would be semantically correct to ignore bit 7 explicitly for SD cards, and hopefully we'd eventually be able to implement the negotiation and support low voltage VDD when the controller and card support it. --phil
