Andrew, Benjamin, Rob, Thanks for bringing up the set of patches and a great discussion. After going through the thread I figured that I'd like to share a few things we needed to hack when programming several BMC boards: - Debug UART enable/mux - Disable GPIO D/E passthrough (I think this is supported by the current pinctrl driver) - RMII/RGMII strapping - iLPC2AHB control - SPI master mux select - Various SuperIO configurations As for the discussion whether these belong to a platform driver or device tree nodes, I think in an ideal world all these configurations could be nicely grouped and abstracted in a platform kernel driver (or drivers). However in reality think this as an "M * N" problem: there are M variants of BMCs and N different platforms built with these BMCs. Each platform-BMC combination is going to have its own quirks and slightly different requirements in BMC "tunables". Were there a kernel driver for the M BMC variants, it would inevitably have a lot of churn due to the different needs of the platforms. What I like about the device tree approach is the expressiveness of the format and the ability to specify non-conflicting initial values easily. Sometimes we need initial values for these parameters set before running userspace, and setting such values in device tree is easier than using #defines or kernel parameters. On Thu, Jul 19, 2018 at 9:57 PM Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx> wrote: > > On Fri, 2018-07-20 at 09:37 +0930, Andrew Jeffery wrote: > > > > > > Andrew, can you start with a list that shows what you expect us to need > > > on our systems ? > > > > > > > Okay, our Witherspoon and Romulus platforms containing the ASPEED AST2500 currently need the following tuneables exposed: > > > > > From the SCU: > > > > - Debug UART enable > > - VGA DAC mux > > - VGA scratch registers 0-7 > > - LPC SuperIO decode enable > > - VGA MMIO decode enable > > > > > From the LPC controller: > > > > - iLPC2AHB enable > > - SuperIO scratch registers 0x20-0x2f > > > > (The LPC controller is just as much of a collection of random bits as the SCU) > > > > Lastly, our Palmetto platform uses an AST2400 which has fewer features compared to the AST2500. Its tuneable list is the same as the above with the exception of "Debug UART enable". > > > > Tuneables that we may need to expose in the future include: > > > > > From the SCU: > > > > - PCI VID/DID for the BMC PCIe device > > - VGA device enable (may need to be disabled if the platform contains a discrete graphics processor) > > Additionally there's a bunch of resigters controlling the mapping of > various MMIO regions of the BMC PCIe device to portions of the BMC > address space. I'm not sure what's the best way to handle that. > > This specific set might require a dedicated device as a subnode of > the SCU in the DT that contains all the mappings as properties... > > That or we consider them static enough and just whack it in u-boot. > > > > From the LPC controller: > > > > - UART mux > > > > Alexander, Eugene, can you chime in with your platforms' needs? > > > > Cheers, > > > > Andrew -- Regards, Kun
