jtag/drivers/bcm2835gpio: don't touch pad setting on /dev/gpiomem

The pads were configured at a wrong memory address
if /dev/gpiomem was mapped.

The pad setting registers are not accessible in mapped /dev/gpiomem,
disable the pads setting if the driver doesn't open /dev/mem.

While on it, do not fail the driver initialization if pad mapping fails
- just emit a warning and work with unchanged pad setting.

Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Change-Id: I0bce76cade8f7efd75efd9087a7d9ba6511a6239
Reviewed-on: https://review.openocd.org/c/openocd/+/7684
Tested-by: jenkins
Reviewed-by: Jonathan Bell <jonathan@raspberrypi.com>
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>

2 files changed, 28 insertions, 12 deletions

diff --git a/doc/openocd.texi b/doc/openocd.texi
index f32ef34..f27e17c 100644
--- a/doc/openocd.texi
+++ b/doc/openocd.texi
@@ -3292,8 +3292,12 @@ configuration on exit.
 GPIO numbers >= 32 can't be used for performance reasons. GPIO configuration is
 handled by the generic command @ref{adapter gpio, @command{adapter gpio}}.
 
+/dev/gpiomem is preferred for GPIO mapping with fallback to /dev/mem.
+If /dev/mem is used GPIO 0-27 pads are set to the limited
+slew rate and drive strength is reduced to 4 mA (2 mA on RPi 4).
+
 See @file{interface/raspberrypi-native.cfg} for a sample config and
-pinout.
+@file{interface/raspberrypi-gpio-connector.cfg} for pinout.
 
 @deffn {Config Command} {bcm2835gpio speed_coeffs} @var{speed_coeff} @var{speed_offset}
 Set SPEED_COEFF and SPEED_OFFSET for delay calculations. If unspecified,
diff --git a/src/jtag/drivers/bcm2835gpio.c b/src/jtag/drivers/bcm2835gpio.c
index 879ca3c..16c76cd 100644
--- a/src/jtag/drivers/bcm2835gpio.c
+++ b/src/jtag/drivers/bcm2835gpio.c
@@ -409,10 +409,13 @@ static int bcm2835gpio_init(void)
 		return ERROR_JTAG_INIT_FAILED;
 	}
 
+	bool pad_mapping_possible = false;
+
 	dev_mem_fd = open("/dev/gpiomem", O_RDWR | O_SYNC);
 	if (dev_mem_fd < 0) {
 		LOG_DEBUG("Cannot open /dev/gpiomem, fallback to /dev/mem");
 		dev_mem_fd = open("/dev/mem", O_RDWR | O_SYNC);
+		pad_mapping_possible = true;
 	}
 	if (dev_mem_fd < 0) {
 		LOG_ERROR("open: %s", strerror(errno));
@@ -428,21 +431,28 @@ static int bcm2835gpio_init(void)
 		return ERROR_JTAG_INIT_FAILED;
 	}
 
-	pads_base = mmap(NULL, sysconf(_SC_PAGE_SIZE), PROT_READ | PROT_WRITE,
+	/* TODO: move pads config to a separate utility */
+	if (pad_mapping_possible) {
+		pads_base = mmap(NULL, sysconf(_SC_PAGE_SIZE), PROT_READ | PROT_WRITE,
 				MAP_SHARED, dev_mem_fd, BCM2835_PADS_GPIO_0_27);
 
-	if (pads_base == MAP_FAILED) {
-		LOG_ERROR("mmap: %s", strerror(errno));
-		bcm2835gpio_munmap();
-		close(dev_mem_fd);
-		return ERROR_JTAG_INIT_FAILED;
+		if (pads_base == MAP_FAILED) {
+			LOG_ERROR("mmap pads: %s", strerror(errno));
+			LOG_WARNING("Continuing with unchanged GPIO pad settings (drive strength and slew rate)");
+		}
+	} else {
+		pads_base = MAP_FAILED;
 	}
 
 	close(dev_mem_fd);
 
-	/* set 4mA drive strength, slew rate limited, hysteresis on */
-	initial_drive_strength_etc = pads_base[BCM2835_PADS_GPIO_0_27_OFFSET] & 0x1f;
-	pads_base[BCM2835_PADS_GPIO_0_27_OFFSET] = 0x5a000008 + 1;
+	if (pads_base != MAP_FAILED) {
+		/* set 4mA drive strength, slew rate limited, hysteresis on */
+		initial_drive_strength_etc = pads_base[BCM2835_PADS_GPIO_0_27_OFFSET] & 0x1f;
+LOG_INFO("initial pads conf %08x", pads_base[BCM2835_PADS_GPIO_0_27_OFFSET]);
+		pads_base[BCM2835_PADS_GPIO_0_27_OFFSET] = 0x5a000008 + 1;
+LOG_INFO("pads conf set to %08x", pads_base[BCM2835_PADS_GPIO_0_27_OFFSET]);
+	}
 
 	/* Configure JTAG/SWD signals. Default directions and initial states are handled
 	 * by adapter.c and "adapter gpio" command.
@@ -513,8 +523,10 @@ static int bcm2835gpio_quit(void)
 	restore_gpio(ADAPTER_GPIO_IDX_SRST);
 	restore_gpio(ADAPTER_GPIO_IDX_LED);
 
-	/* Restore drive strength. MSB is password ("5A") */
-	pads_base[BCM2835_PADS_GPIO_0_27_OFFSET] = 0x5A000000 | initial_drive_strength_etc;
+	if (pads_base != MAP_FAILED) {
+		/* Restore drive strength. MSB is password ("5A") */
+		pads_base[BCM2835_PADS_GPIO_0_27_OFFSET] = 0x5A000000 | initial_drive_strength_etc;
+	}
 	bcm2835gpio_munmap();
 
 	return ERROR_OK;