surface3-spi: workaround: disable DMA mode to avoid crash by default

On Arch Linux kernel at least after 4.19, touch input is broken after suspend
(s2idle).

        kern  :err   : [  +0.203408] Surface3-spi spi-MSHW0037:00: SPI transfer timed out

On recent stable Arch Linux kernel (at least after 5.1), touch input will
crash after the first touch.

        kern  :err   : [  +0.203592] Surface3-spi spi-MSHW0037:00: SPI transfer timed out
        kern  :err   : [  +0.000173] spi_master spi1: failed to transfer one message from queue

I found on an affected system (Arch Linux kernel, etc.), the touchscreen
driver uses DMA mode by default. Then, we found some kernels with different
kernel config (5.1 kernel config from Jakeday [1] or Chromium OS kernel
chromeos-4.19 [2]) will use PIO mode by default and no such issues there.

So, this commit disables DMA mode on the touchscreen driver side as a quick
workaround to avoid touch input crash.
We may need to properly set up DMA mode to use the touchscreen driver with
DMA mode.

You can still switch DMA/PIO mode if you want:

  switch to DMA mode (maybe broken)
        echo 1 | sudo tee /sys/module/surface3_spi/parameters/use_dma
  back to PIO mode
        echo 0 | sudo tee /sys/module/surface3_spi/parameters/use_dma

Link to issue: jakeday/linux-surface#596

References:
[1] https://github.com/jakeday/linux-surface/blob/master/configs/5.1/config
[2] https://chromium.googlesource.com/chromiumos/third_party/kernel/+/refs/heads/chromeos-4.19

Tested on Arch Linux 5.4.1 with Surface 3, which will use DMA by default.
This commit made the driver use PIO by default and no touch input crash.
Also tested on chromeos-4.19 4.19.90 with Surface 3, which will use PIO by default
even without this commit. After this commit, it still uses PIO and confirmed
no functional changes regarding touch input.

More details:
  We can confirm which mode the touchscreen driver uses; first, enable
  debug output:

        echo "file drivers/spi/spi-pxa2xx.c +p" | sudo tee /sys/kernel/debug/dynamic_debug/control
        echo "file drivers/input/touchscreen/surface3_spi.c +p" | sudo tee /sys/kernel/debug/dynamic_debug/control

  Then, try to make a touch input and see dmesg log

        (On Arch Linux kernel, uses DMA)
        kern  :debug : [  +0.006383] Surface3-spi spi-MSHW0037:00: 7692307 Hz actual, DMA
        kern  :debug : [  +0.000495] Surface3-spi spi-MSHW0037:00: surface3_spi_irq_handler received
	-> ff ff ff ff a5 5a e7 7e 01 d2 00 80 01 03 03 18 00 e4 01 00 04 1a 04 1a e3 0c e3 0c b0 00
	c5 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff

        (On the kernels I referenced above, uses PIO)
        kern  :debug : [  +0.009260] Surface3-spi spi-MSHW0037:00: 7692307 Hz actual, PIO
        kern  :debug : [  +0.001105] Surface3-spi spi-MSHW0037:00: surface3_spi_irq_handler received
	-> ff ff ff ff a5 5a e7 7e 01 d2 00 80 01 03 03 24 00 e4 01 00 58 0b 58 0b 83 12 83 12 26 01
	95 01 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff

drivers/input/touchscreen/surface3_spi.c

@@ -25,6 +25,12 @@
 #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];
@@ -326,6 +332,13 @@ 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;
@@ -368,6 +381,19 @@ 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;
 }