Hi, On 3/28/2018 4:22 AM, Doug Anderson wrote: > Hi, > > On Thu, Mar 22, 2018 at 11:11 PM, Manu Gautam <mgautam@xxxxxxxxxxxxxx> wrote: >> There are two QUSB2 PHYs present on sdm845. Update PHY >> registers programming for both the PHYs related to >> electrical parameters to improve eye diagram. > This tuning difference is truly associated with the SoC itself? Are > you sure? Are the two different PHYs in the SoC somehow using > different silicon processes? ...or is one close to another IP block > that is noisy? ...or something else to account for this difference? > > It seems more likely that this tuning difference is associated with > the board. If you're _certain_ this is really due to internal SoC > differences you'll have to come up with some darn good evidence to > convince me... This difference must be due to board only. > > If the tuning is truly associated with the board then: > > 1. You should have a single device tree compatible string. IMHO it > should contain the name of the SoC in it, so "qcom,sdm845-qusb2-phy". > It's generally OK to name something in Linux using the name of the > first thing that happened to support it in Linux (even if later > processors use the exact same component). Leaving it as just > "qcom,qusb2-v2-phy" is OK with me too if that's what everyone wants. I will remove "qcom,qusb2-v2-phy" as I don't expect any users of that. > > > 2. You should figure out how to describe the needed board-to-board > tuning in device tree. > > The only two differences you have right now are: > > QUSB2PHY_IMP_CTRL1: 0 => 0x8 > QUSB2PHY_PORT_TUNE1: 0x30 => 0x48 > > I'm not sure I found all the correct documentation for the PHY (the > docs I have say that "TUNE1" bit 3 is "reserved") so I can't come up > with all of these for you. But I think I found the difference > accounting for the upper nybble of TUNE1 changing from 0x3 to 0x4. > For this, I think you'd want a device tree property like: > > qcom,hstx_trim_mv > > ...and the values of that property would be the values from 800 to 950 > in 8 steps, or [800, 821, 842, 864, 885, 907, 928, 950]. > > You'd want to do similar things for the other differences. > > You don't need to encode every possible difference right now. When > you come up with something that needs to be different you add a new > optional device tree property (defaulting to whatever the driver used > to do) to describe your new property. Sure. I will come up with separate device tree properties to specify board-to-board differences in PHY tuning. > > -Doug -- The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project -- To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
