From patchwork Fri Feb 11 21:22:56 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Danilo Krummrich X-Patchwork-Id: 541930 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6FF38C433F5 for ; Fri, 11 Feb 2022 21:31:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1353650AbiBKVbn (ORCPT ); Fri, 11 Feb 2022 16:31:43 -0500 Received: from mxb-00190b01.gslb.pphosted.com ([23.128.96.19]:49502 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1353671AbiBKVbn (ORCPT ); Fri, 11 Feb 2022 16:31:43 -0500 Received: from hs01.dk-develop.de (hs01.dk-develop.de [IPv6:2a02:c207:3002:6234::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A10D5C61 for ; Fri, 11 Feb 2022 13:31:41 -0800 (PST) From: Danilo Krummrich To: dmitry.torokhov@gmail.com, linux-input@vger.kernel.org, linux-kernel@vger.kernel.org Cc: linus.walleij@linaro.org, Danilo Krummrich Subject: [PATCH 1/3] input: ps2-gpio: use ktime for IRQ timekeeping Date: Fri, 11 Feb 2022 22:22:56 +0100 Message-Id: <20220211212258.80345-2-danilokrummrich@dk-develop.de> In-Reply-To: <20220211212258.80345-1-danilokrummrich@dk-develop.de> References: <20220211212258.80345-1-danilokrummrich@dk-develop.de> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-input@vger.kernel.org Using jiffies for the IRQ timekeeping is not sufficient for two reasons: (1) Usually jiffies have a resolution of 1ms to 10ms. The IRQ intervals based on the clock frequency of PS2 protocol specification (10kHz - 16.7kHz) are between ~60us and 100us only. Therefore only those IRQ intervals can be detected which are either at the end of a transfer or are overly delayed. While this is sufficient in most cases, since we have quite a lot of ways to detect faulty transfers, it can produce false positives in rare cases: When the jiffies value changes right between two interrupt that are in time, we wrongly assume that we missed one or more clock cycles. (2) Some gpio controllers (e.g. the one in the bcm283x chips) may generate spurious IRQs when processing interrupts in the frequency given by PS2 devices. Both issues can be fixed by using ktime resolution for IRQ timekeeping. However, it is still possible to miss clock cycles without detecting them. When the PS2 device generates the falling edge of the clock signal we have between ~30us and 50us to sample the data line, because after this time we reach the next rising edge at which the device changes the data signal already. But, the only thing we can detect is whether the IRQ interval is within the given period. Therefore it is possible to have an IRQ latency greater than ~30us to 50us, sample the wrong bit on the data line and still be on time with the next IRQ. However, this can only happen when within a given transfer the IRQ latency increases slowly. ___ ______ ______ ______ ___ \ / \ / \ / \ / \ / \ / \ / \ / \______/ \______/ \______/ \______/ |-----------------| |--------| 60us/100us 30us/50us Signed-off-by: Danilo Krummrich --- drivers/input/serio/ps2-gpio.c | 81 ++++++++++++++++++++++++++++------ 1 file changed, 67 insertions(+), 14 deletions(-) diff --git a/drivers/input/serio/ps2-gpio.c b/drivers/input/serio/ps2-gpio.c index 8970b49ea09a..7fef4176bdd1 100644 --- a/drivers/input/serio/ps2-gpio.c +++ b/drivers/input/serio/ps2-gpio.c @@ -19,6 +19,7 @@ #include #include #include +#include #define DRIVER_NAME "ps2-gpio" @@ -44,6 +45,29 @@ #define PS2_CMD_RESEND 0xfe +/* The PS2 protocol specifies a clock frequency between 10kHz and 16.7kHz, + * therefore the maximal interrupt interval should be 100us and the minimum + * interrupt interval should be ~60us. Let's allow +/- 20us for frequency + * deviations and interrupt latency. + * + * The data line must be samples after ~30us to 50us after the falling edge, + * since the device updates the data line at the rising edge. + * + * ___ ______ ______ ______ ___ + * \ / \ / \ / \ / + * \ / \ / \ / \ / + * \______/ \______/ \______/ \______/ + * + * |-----------------| |--------| + * 60us/100us 30us/50us + */ +#define PS2_CLK_FREQ_MIN_HZ 10000 +#define PS2_CLK_FREQ_MAX_HZ 16700 +#define PS2_CLK_MIN_INTERVAL_US ((1000 * 1000) / PS2_CLK_FREQ_MAX_HZ) +#define PS2_CLK_MAX_INTERVAL_US ((1000 * 1000) / PS2_CLK_FREQ_MIN_HZ) +#define PS2_IRQ_MIN_INTERVAL_US (PS2_CLK_MIN_INTERVAL_US - 20) +#define PS2_IRQ_MAX_INTERVAL_US (PS2_CLK_MAX_INTERVAL_US + 20) + struct ps2_gpio_data { struct device *dev; struct serio *serio; @@ -59,6 +83,8 @@ struct ps2_gpio_data { struct completion tx_done; struct mutex tx_mutex; struct delayed_work tx_work; + ktime_t tx_start; + ktime_t tx_end; }; static int ps2_gpio_open(struct serio *serio) @@ -118,6 +144,7 @@ static void ps2_gpio_tx_work_fn(struct work_struct *work) struct ps2_gpio_data, tx_work); + drvdata->tx_start = ktime_get(); enable_irq(drvdata->irq); gpiod_direction_output(drvdata->gpio_data, 0); gpiod_direction_input(drvdata->gpio_clk); @@ -128,20 +155,33 @@ static irqreturn_t ps2_gpio_irq_rx(struct ps2_gpio_data *drvdata) unsigned char byte, cnt; int data; int rxflags = 0; - static unsigned long old_jiffies; + static ktime_t t_last, t_now; + s64 us_delta; byte = drvdata->rx_byte; cnt = drvdata->rx_cnt; - if (old_jiffies == 0) - old_jiffies = jiffies; + t_now = ktime_get(); + if (t_last == 0) + t_last = t_now; - if ((jiffies - old_jiffies) > usecs_to_jiffies(100)) { + /* We need to consider spurious interrupts happening right after a TX xfer + * finished. + */ + if (unlikely(ktime_us_delta(t_now, drvdata->tx_end) < + PS2_IRQ_MIN_INTERVAL_US)) + goto end; + + us_delta = ktime_us_delta(t_now, t_last); + if (us_delta > PS2_IRQ_MAX_INTERVAL_US && cnt) { dev_err(drvdata->dev, "RX: timeout, probably we missed an interrupt\n"); goto err; + } else if (us_delta < PS2_IRQ_MIN_INTERVAL_US && t_now != t_last) { + /* Ignore spurious IRQs. */ + goto end; } - old_jiffies = jiffies; + t_last = t_now; data = gpiod_get_value(drvdata->gpio_data); if (unlikely(data < 0)) { @@ -205,7 +245,7 @@ static irqreturn_t ps2_gpio_irq_rx(struct ps2_gpio_data *drvdata) goto err; } cnt = byte = 0; - old_jiffies = 0; + goto end; /* success */ default: dev_err(drvdata->dev, "RX: got out of sync with the device\n"); @@ -217,7 +257,6 @@ static irqreturn_t ps2_gpio_irq_rx(struct ps2_gpio_data *drvdata) err: cnt = byte = 0; - old_jiffies = 0; __ps2_gpio_write(drvdata->serio, PS2_CMD_RESEND); end: drvdata->rx_cnt = cnt; @@ -229,20 +268,34 @@ static irqreturn_t ps2_gpio_irq_tx(struct ps2_gpio_data *drvdata) { unsigned char byte, cnt; int data; - static unsigned long old_jiffies; + static ktime_t t_last, t_now; + s64 us_delta; cnt = drvdata->tx_cnt; byte = drvdata->tx_byte; - if (old_jiffies == 0) - old_jiffies = jiffies; + t_now = ktime_get(); + if (t_last == 0) + t_last = t_now; + + /* There might be pending IRQs since we disabled IRQs in __ps2_gpio_write(). + * We can expect at least one clock period until the device generates the + * first falling edge after releasing the clock line. + */ + if (unlikely(ktime_us_delta(t_now, drvdata->tx_start) < + PS2_CLK_MIN_INTERVAL_US)) + goto end; - if ((jiffies - old_jiffies) > usecs_to_jiffies(100)) { + us_delta = ktime_us_delta(t_now, t_last); + if (us_delta > PS2_IRQ_MAX_INTERVAL_US && cnt > 1) { dev_err(drvdata->dev, "TX: timeout, probably we missed an interrupt\n"); goto err; + } else if (us_delta < PS2_IRQ_MIN_INTERVAL_US && t_now != t_last) { + /* Ignore spurious IRQs. */ + goto end; } - old_jiffies = jiffies; + t_last = t_now; switch (cnt) { case PS2_START_BIT: @@ -283,11 +336,11 @@ static irqreturn_t ps2_gpio_irq_tx(struct ps2_gpio_data *drvdata) goto err; } + drvdata->tx_end = ktime_get(); drvdata->mode = PS2_MODE_RX; complete(&drvdata->tx_done); cnt = 1; - old_jiffies = 0; goto end; /* success */ default: /* Probably we missed the stop bit. Therefore we release data @@ -303,7 +356,6 @@ static irqreturn_t ps2_gpio_irq_tx(struct ps2_gpio_data *drvdata) err: cnt = 1; - old_jiffies = 0; gpiod_direction_input(drvdata->gpio_data); __ps2_gpio_write(drvdata->serio, drvdata->tx_byte); end: @@ -399,6 +451,7 @@ static int ps2_gpio_probe(struct platform_device *pdev) drvdata->serio = serio; drvdata->dev = dev; drvdata->mode = PS2_MODE_RX; + drvdata->tx_end = 0; /* Tx count always starts at 1, as the start bit is sent implicitly by * host-to-device communication initialization. From patchwork Fri Feb 11 21:22:57 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Danilo Krummrich X-Patchwork-Id: 541931 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 326BCC433FE for ; Fri, 11 Feb 2022 21:31:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241594AbiBKVbn (ORCPT ); Fri, 11 Feb 2022 16:31:43 -0500 Received: from mxb-00190b01.gslb.pphosted.com ([23.128.96.19]:49500 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1353650AbiBKVbn (ORCPT ); Fri, 11 Feb 2022 16:31:43 -0500 Received: from hs01.dk-develop.de (hs01.dk-develop.de [IPv6:2a02:c207:3002:6234::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B57C9C63 for ; Fri, 11 Feb 2022 13:31:41 -0800 (PST) From: Danilo Krummrich To: dmitry.torokhov@gmail.com, linux-input@vger.kernel.org, linux-kernel@vger.kernel.org Cc: linus.walleij@linaro.org, Danilo Krummrich Subject: [PATCH 2/3] input: ps2-gpio: remove tx timeout from ps2_gpio_irq_tx() Date: Fri, 11 Feb 2022 22:22:57 +0100 Message-Id: <20220211212258.80345-3-danilokrummrich@dk-develop.de> In-Reply-To: <20220211212258.80345-1-danilokrummrich@dk-develop.de> References: <20220211212258.80345-1-danilokrummrich@dk-develop.de> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-input@vger.kernel.org Actually, there's no extra clock pulse to wait for. The assumption of an extra clock pulse was mistakenly derived from the fact that by the time this driver was introduced the GPIO controller of the test machine (bcm2835) generated spurious interrupts. Since now spurious interrupts are handled properly this can and must be removed in order to make TX xfers work properly. While at it, remove duplicate gpiod_direction_input(). The data gpio must already be configured to act as input when receiving the ACK bit. This patch is tested with the original hardware (peripherals and board) the driver was developed on. Signed-off-by: Danilo Krummrich --- drivers/input/serio/ps2-gpio.c | 9 +-------- 1 file changed, 1 insertion(+), 8 deletions(-) diff --git a/drivers/input/serio/ps2-gpio.c b/drivers/input/serio/ps2-gpio.c index 7fef4176bdd1..336928a8a127 100644 --- a/drivers/input/serio/ps2-gpio.c +++ b/drivers/input/serio/ps2-gpio.c @@ -37,8 +37,7 @@ #define PS2_DATA_BIT7 8 #define PS2_PARITY_BIT 9 #define PS2_STOP_BIT 10 -#define PS2_TX_TIMEOUT 11 -#define PS2_ACK_BIT 12 +#define PS2_ACK_BIT 11 #define PS2_DEV_RET_ACK 0xfa #define PS2_DEV_RET_NACK 0xfe @@ -323,13 +322,7 @@ static irqreturn_t ps2_gpio_irq_tx(struct ps2_gpio_data *drvdata) /* release data line to generate stop bit */ gpiod_direction_input(drvdata->gpio_data); break; - case PS2_TX_TIMEOUT: - /* Devices generate one extra clock pulse before sending the - * acknowledgment. - */ - break; case PS2_ACK_BIT: - gpiod_direction_input(drvdata->gpio_data); data = gpiod_get_value(drvdata->gpio_data); if (data) { dev_warn(drvdata->dev, "TX: received NACK, retry\n"); From patchwork Fri Feb 11 21:22:58 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Danilo Krummrich X-Patchwork-Id: 542664 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0672FC4332F for ; Fri, 11 Feb 2022 21:31:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1353671AbiBKVbo (ORCPT ); Fri, 11 Feb 2022 16:31:44 -0500 Received: from mxb-00190b01.gslb.pphosted.com ([23.128.96.19]:49504 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1353697AbiBKVbn (ORCPT ); Fri, 11 Feb 2022 16:31:43 -0500 X-Greylist: delayed 512 seconds by postgrey-1.37 at lindbergh.monkeyblade.net; Fri, 11 Feb 2022 13:31:41 PST Received: from hs01.dk-develop.de (hs01.dk-develop.de [173.249.23.66]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B577FC62 for ; Fri, 11 Feb 2022 13:31:41 -0800 (PST) From: Danilo Krummrich To: dmitry.torokhov@gmail.com, linux-input@vger.kernel.org, linux-kernel@vger.kernel.org Cc: linus.walleij@linaro.org, Danilo Krummrich Subject: [PATCH 3/3] input: ps2-gpio: don't send rx data before the stop bit Date: Fri, 11 Feb 2022 22:22:58 +0100 Message-Id: <20220211212258.80345-4-danilokrummrich@dk-develop.de> In-Reply-To: <20220211212258.80345-1-danilokrummrich@dk-develop.de> References: <20220211212258.80345-1-danilokrummrich@dk-develop.de> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-input@vger.kernel.org Sending the data before processing the stop bit from the device already saves the data of the current xfer in case the stop bit is missed. However, when TX xfers are enabled this introduces a race condition when a peripheral driver using the bus immediately requests a TX xfer from IRQ context. Therefore the data must be send after receiving the stop bit, although it is possible the data is lost when missing the stop bit. Signed-off-by: Danilo Krummrich --- drivers/input/serio/ps2-gpio.c | 21 ++++++++------------- 1 file changed, 8 insertions(+), 13 deletions(-) diff --git a/drivers/input/serio/ps2-gpio.c b/drivers/input/serio/ps2-gpio.c index 336928a8a127..460d520ac865 100644 --- a/drivers/input/serio/ps2-gpio.c +++ b/drivers/input/serio/ps2-gpio.c @@ -217,6 +217,13 @@ static irqreturn_t ps2_gpio_irq_rx(struct ps2_gpio_data *drvdata) if (!drvdata->write_enable) goto err; } + break; + case PS2_STOP_BIT: + /* stop bit should be high */ + if (unlikely(!data)) { + dev_err(drvdata->dev, "RX: stop bit should be high\n"); + goto err; + } /* Do not send spurious ACK's and NACK's when write fn is * not provided. @@ -228,21 +235,9 @@ static irqreturn_t ps2_gpio_irq_rx(struct ps2_gpio_data *drvdata) break; } - /* Let's send the data without waiting for the stop bit to be - * sent. It may happen that we miss the stop bit. When this - * happens we have no way to recover from this, certainly - * missing the parity bit would be recognized when processing - * the stop bit. When missing both, data is lost. - */ serio_interrupt(drvdata->serio, byte, rxflags); dev_dbg(drvdata->dev, "RX: sending byte 0x%x\n", byte); - break; - case PS2_STOP_BIT: - /* stop bit should be high */ - if (unlikely(!data)) { - dev_err(drvdata->dev, "RX: stop bit should be high\n"); - goto err; - } + cnt = byte = 0; goto end; /* success */