On Mon, May 18, 2020 at 04:18:43PM +0200, Drew Fustini wrote: > On Mon, May 18, 2020 at 09:11:07AM +0200, Linus Walleij wrote: > > On Fri, May 8, 2020 at 6:57 PM Drew Fustini <drew@xxxxxxxxxxxxxxx> wrote: > > > > > Add gpio-line-names properties to the gpio controller nodes. > > > BeagleBone boards have P8 and P9 headers [0] which expose many the > > > AM3358 SoC balls to stacking expansion boards called "capes", or to > > > other external connections like jumper wires to a breadboard. > > > > > > Many of the P8/P9 header pins can muxed to a gpio line. The > > > gpio-line-names describe which P8/P9 pin that line goes to and the > > > default mux for that P8/P9 pin. Some lines are not routed to the > > > P8/P9 headers, but instead are dedicated to some functionality such as > > > status LEDs. The line name will indicate this. Some line names are > > > left empty as the corresponding AM3358 balls are not connected. > > > > > > The goal is to make it easier for a user viewing the output of gpioinfo > > > to determine which P8/P9 pin is connected to a line. The output of > > > gpioinfo on a BeagleBone Black will now look like this: > > > > > > gpiochip0 - 32 lines: > > > line 0: "ethernet" unused input active-high > > > line 1: "ethernet" unused input active-high > > > > Why are the ethernet lines not tagged with respective signal name > > when right below the SPI lines are explicitly tagged with > > sclk, cs0 etc? > > > > Ethernet is usually RGMII and has signal names like > > tx_clk, tx_d0, tx_en etc. > > Thank you for the feedback, Linus. > > My desire is to communicate that the AM3358 balls corresponding to these > GPIO lines are being used for Ethernet and not exposed to the P8 and P9 > expansion headers. > > I am happy to switch these labels to the actual Ethernet signals such as > RGMII and MDIO signal names if you think that is better. > > For example, AM3358 ZCZ ball M17 is both gpio0_0 and mdio_data [0]. On > BeagleBone, the ball is routed to the Ethernet PHY and used for MDIO [1] > Thus gpiochio 0 line 0 is not connected to the P8 or P9 expansion header. > > Which of the following line name would be best? > > 1) "[MDIO_DATA]" > > precise signal name, placed in brackets to denote is not possible to > use as GPIO on the P8 or P9 headers > > 2) "[ethernet]" > > instead of the precise signal name, just indicate that it is used for > Ethernet and is not usable for GPIO on the P8 or P9 headers > > 3) "" > > no label as this gpio line is not connected to the P8/P9 and is > hardwired in the PCB layout for Ethernet (MDIO). > > > Also some lines seem to be tagged with the pin number > > like P9_22, P2_21 below, it seems a bit inconsistent > > to have much information on some pins and very sketchy > > information on some. > > The goal for these line names is make it easier for a BeagleBone user to > identify which GPIO lines are connected to the P8 and P9 expansion > headers. Our users are most likely to refer to cape-headers.png [2] as > it is part of the bone101 out-of-the-box tutorial [3]. > > Some GPIO lines are free to be used for GPIO in the default > configuration. For example, gpiochip 1 line 12 is connected to P8_12 > and it is not used by another peripheral by default. I used the label: > "P8_12 gpio" > > However, gpiochip 1 line 0 is connected to P8_25 but is also used by the > on-board eMMC. The eMMc is enabled by default so this line can not be > used for GPIO unless the user modifies the pinmux in the device tree. > > Thus, I used this label: "P8_25 emmc" > > Maybe a better label would be "P8_25 [EMMC]"? > > > > > > line 18: "usb" unused input active-high > > > line 19: "hdmi" unused input active-high > > > > Similar comments for these. > > > These are similar to the Ethernet MDIO example above. The balls > corresponding to these GPIO lines are not connected to the P8 or P9 > headers and are hardwired on the PCB for other peripherals like USB > and HDMI. > > For example, gpiochip 0 line 18 is USB0_DRVVBUS so I simplified it to > "usb" to indicate it can not be used for GPIO. Maybe "[USB]" is better? > > gpiochip 0 line 19 is AM3358 ZCZ ball A15 and the BeagleBone Black > schematic shows that this is connected to the CEC clock for the HDMI > framer [4]. I though "hdmi" was a nice way to summarize that this is > used for HDMI and can not be changed, though maybe "[HDMI]" is better > or no label at all. > > In conclusion, the motivation of these line names is to be a quick > reference for a user to find GPIO lines on the P8 and P9 headers. > > Thanks, > Drew > > [0] http://www.ti.com/lit/ds/symlink/am3358.pdf > [1] https://github.com/beagleboard/beaglebone-black/wiki/System-Reference-Manual#ethernet-processor-interface > [2] http://beagleboard.org/static/images/cape-headers.png > [3] https://beagleboard.org/Support/bone101 > [4] https://github.com/beagleboard/beaglebone-black/blob/master/BBB_SCH.pdf > I've posted a v2 which I hope improves the intent of the line names. [0] I'm happy to integrate any feedback and create a v3 - especially if it is prefered for me to list the specific peripherial signals instead of an abstract term like "[ethernet]" or "[emmc]". This is for lines that can not be used because they are not routed to the expansion headers. thanks, drew [0] https://lore.kernel.org/linux-omap/20200520214757.GA362547@x1/T/#u
