arm64: dts: apple: Replace UART clocking TODO with proper documentation#550
Open
statick88 wants to merge 1 commit into
Open
arm64: dts: apple: Replace UART clocking TODO with proper documentation#550statick88 wants to merge 1 commit into
statick88 wants to merge 1 commit into
Conversation
The TODO comments in the Apple SoC device trees speculated about a
"third selectable clock" for the S5L UART. Investigation of the
Samsung-compatible UART driver (samsung_tty.c) shows:
- The driver sets num_clks = 1 for the S5L variant, meaning it only
searches for one baud clock ("clk_uart_baud0").
- The baud divisor formula is: quot = (rate + (8 * baud)) / (16 * baud)
- With 24 MHz clkref, standard baud rates achieve <0.2% error
(e.g., 115200 baud: 0.16% error).
Both the "uart" (peripheral bus) and "clk_uart_baud0" (baud rate
generator) clocks correctly use the 24 MHz reference clock. No third
clock is needed or supported by the driver.
Replace the speculative TODO with a comment documenting this finding
across all 7 affected SoC dtsi files.
Signed-off-by: Diego Saavedra <dsaavedra88@gmail.com>
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
1 participant
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
Summary
Replace speculative TODO comments about UART clocking in 7 Apple Silicon
.dtsifiles with proper documentation explaining why<&clkref>(24 MHz) is correct.Background
The TODO comments (
figure out the clocking properly, there may be a third selectable clock) were misleading. Analysis of the Samsung-compatible UART driver (samsung_tty.c) shows:num_clks = 1for the S5L variant, only searching for one baud clock (clk_uart_baud0).quot = (rate + (8 * baud)) / (16 * baud)Both clocks correctly use the 24 MHz reference clock. No third clock is needed or supported by the driver.
Changes
.dtsifiles:t8103.dtsi,t8112.dtsi,t8122.dtsi,t6030.dtsi,t600x-die0.dtsi,t602x-die0.dtsi,t6031-die0.dtsicheckpatch.pl
Signed-off-by: Diego Saavedra dsaavedra88@gmail.com