linux-surface/patches/4.19/0002-surface3-spi.patch

From 06e4d51c83a77d54ca5b1d402fb57554c51d3926 Mon Sep 17 00:00:00 2001
From: kitakar5525 <34676735+kitakar5525@users.noreply.github.com>
Date: Fri, 6 Dec 2019 23:10:30 +0900
Subject: [PATCH 02/10] surface3-spi

---
 drivers/input/touchscreen/surface3_spi.c | 26 ++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/drivers/input/touchscreen/surface3_spi.c b/drivers/input/touchscreen/surface3_spi.c
index 5db0f1c4ef38..8935ddbc2357 100644
--- a/drivers/input/touchscreen/surface3_spi.c
+++ b/drivers/input/touchscreen/surface3_spi.c
@@ -29,6 +29,12 @@
 #define SURFACE3_REPORT_TOUCH	0xd2
 #define SURFACE3_REPORT_PEN	0x16
 
+bool use_dma = false;
+module_param(use_dma, bool, 0644);
+MODULE_PARM_DESC(use_dma,
+				"Disable DMA mode if you encounter touch input crash. "
+				"(default: false, disabled to avoid crash)");
+
 struct surface3_ts_data {
 	struct spi_device *spi;
 	struct gpio_desc *gpiod_rst[2];
@@ -330,6 +336,13 @@ static int surface3_spi_create_pen_input(struct surface3_ts_data *data)
 	return 0;
 }
 
+static bool surface3_spi_can_dma(struct spi_controller *ctlr,
+				struct spi_device *spi,
+				struct spi_transfer *tfr)
+{
+	return use_dma;
+}
+
 static int surface3_spi_probe(struct spi_device *spi)
 {
 	struct surface3_ts_data *data;
@@ -372,6 +385,19 @@ static int surface3_spi_probe(struct spi_device *spi)
 	if (error)
 		return error;
 
+	/*
+	 * Set up DMA
+	 *
+	 * TODO: Currently, touch input with DMA seems to be broken.
+	 * On 4.19 LTS, touch input will crash after suspend.
+	 * On recent stable kernel (at least after 5.1), touch input will crash after
+	 * the first touch. No problem with PIO on those kernels.
+	 * Maybe we need to configure DMA here.
+	 *
+	 * Link to issue: https://github.com/jakeday/linux-surface/issues/596
+	 */
+	spi->controller->can_dma = surface3_spi_can_dma;
+
 	return 0;
 }
 
-- 
2.26.2