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148 lines
4.5 KiB
Diff
148 lines
4.5 KiB
Diff
From b039a10b277af6aeb245e3b791e2dd4ab161698c Mon Sep 17 00:00:00 2001
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From: Jonathan Bell <jonathan@raspberrypi.com>
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Date: Thu, 11 Jan 2024 16:33:22 +0000
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Subject: [PATCH 0849/1085] drivers: w1-gpio: add flag to force read-polling
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while delaying
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On Pi 5, the link to RP1 will bounce in and out of L1 depending on
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inactivity timers at both the RC and EP end. Unfortunately for
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bitbashing 1-wire, this means that on an otherwise idle Pi 5 many of the
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reads/writes to GPIO registers are delayed by up to 8us which causes
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mis-sampling of read data and trashes write bits.
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By issuing dummy reads at a rate greater than the link inactivity
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timeout while spinning on a delay, PCIe stays in L0 which does not incur
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additional latency.
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Signed-off-by: Jonathan Bell <jonathan@raspberrypi.com>
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---
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drivers/w1/masters/w1-gpio.c | 3 +++
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drivers/w1/w1_io.c | 37 ++++++++++++++++++++++++------------
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include/linux/w1.h | 5 +++++
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3 files changed, 33 insertions(+), 12 deletions(-)
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--- a/drivers/w1/masters/w1-gpio.c
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+++ b/drivers/w1/masters/w1-gpio.c
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@@ -90,6 +90,9 @@ static int w1_gpio_probe(struct platform
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if (of_property_present(np, "linux,open-drain"))
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gflags = GPIOD_OUT_LOW;
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+ if (of_property_present(np, "raspberrypi,delay-needs-poll"))
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+ master->delay_needs_poll = true;
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+
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pdev->dev.platform_data = pdata;
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}
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pdata = dev_get_platdata(dev);
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--- a/drivers/w1/w1_io.c
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+++ b/drivers/w1/w1_io.c
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@@ -6,6 +6,7 @@
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#include <asm/io.h>
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#include <linux/delay.h>
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+#include <linux/ktime.h>
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#include <linux/moduleparam.h>
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#include <linux/module.h>
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@@ -36,9 +37,21 @@ static u8 w1_crc8_table[] = {
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116, 42, 200, 150, 21, 75, 169, 247, 182, 232, 10, 84, 215, 137, 107, 53
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};
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-static void w1_delay(unsigned long tm)
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+static void w1_delay(struct w1_master *dev, unsigned long tm)
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{
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- udelay(tm * w1_delay_parm);
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+ ktime_t start, delta;
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+
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+ if (!dev->bus_master->delay_needs_poll) {
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+ udelay(tm * w1_delay_parm);
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+ return;
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+ }
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+
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+ start = ktime_get();
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+ delta = ktime_add(start, ns_to_ktime(1000 * tm * w1_delay_parm));
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+ do {
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+ dev->bus_master->read_bit(dev->bus_master->data);
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+ udelay(1);
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+ } while (ktime_before(ktime_get(), delta));
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}
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static void w1_write_bit(struct w1_master *dev, int bit);
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@@ -77,14 +90,14 @@ static void w1_write_bit(struct w1_maste
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if (bit) {
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dev->bus_master->write_bit(dev->bus_master->data, 0);
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- w1_delay(6);
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+ w1_delay(dev, 6);
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dev->bus_master->write_bit(dev->bus_master->data, 1);
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- w1_delay(64);
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+ w1_delay(dev, 64);
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} else {
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dev->bus_master->write_bit(dev->bus_master->data, 0);
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- w1_delay(60);
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+ w1_delay(dev, 60);
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dev->bus_master->write_bit(dev->bus_master->data, 1);
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- w1_delay(10);
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+ w1_delay(dev, 10);
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}
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if(w1_disable_irqs) local_irq_restore(flags);
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@@ -164,14 +177,14 @@ static u8 w1_read_bit(struct w1_master *
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/* sample timing is critical here */
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local_irq_save(flags);
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dev->bus_master->write_bit(dev->bus_master->data, 0);
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- w1_delay(6);
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+ w1_delay(dev, 6);
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dev->bus_master->write_bit(dev->bus_master->data, 1);
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- w1_delay(9);
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+ w1_delay(dev, 9);
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result = dev->bus_master->read_bit(dev->bus_master->data);
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local_irq_restore(flags);
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- w1_delay(55);
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+ w1_delay(dev, 55);
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return result & 0x1;
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}
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@@ -333,16 +346,16 @@ int w1_reset_bus(struct w1_master *dev)
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* cpu for such a short amount of time AND get it back in
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* the maximum amount of time.
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*/
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- w1_delay(500);
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+ w1_delay(dev, 500);
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dev->bus_master->write_bit(dev->bus_master->data, 1);
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- w1_delay(70);
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+ w1_delay(dev, 70);
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result = dev->bus_master->read_bit(dev->bus_master->data) & 0x1;
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/* minimum 70 (above) + 430 = 500 us
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* There aren't any timing requirements between a reset and
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* the following transactions. Sleeping is safe here.
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*/
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- /* w1_delay(430); min required time */
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+ /* w1_delay(dev, 430); min required time */
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msleep(1);
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}
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--- a/include/linux/w1.h
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+++ b/include/linux/w1.h
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@@ -121,6 +121,9 @@ typedef void (*w1_slave_found_callback)(
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* @dev_id: Optional device id string, which w1 slaves could use for
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* creating names, which then give a connection to the w1 master
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*
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+ * @delay_needs_poll: work around jitter introduced with GPIO controllers
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+ * accessed over PCIe (RP1)
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+ *
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* Note: read_bit and write_bit are very low level functions and should only
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* be used with hardware that doesn't really support 1-wire operations,
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* like a parallel/serial port.
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@@ -155,6 +158,8 @@ struct w1_bus_master {
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u8, w1_slave_found_callback);
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char *dev_id;
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+
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+ bool delay_needs_poll;
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};
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/**
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