enable/disable channels through DCR enable bit

This patch addresses the performance problem reported by Christophe Chanavat (a single call to fdelay_config_pulse takes 2.1ms to complete). The time is spent in driving the GPIO enable line that controls the output stage decoupling. This is done via SPI, and each spi_xfer takes 420us, which add up to the reported delay. The fix leaves the enable pins always on, so the output relay is not used to control whether the outputs are enabled/disabled; it is the DCR enable bit who takes this role instead. This results in an average 8us time for output delay configuration, 3us for output disable. Conflicts: kernel/fd-zio.c

enable/disable channels through DCR enable bit
This patch addresses the performance problem reported by Christophe Chanavat (a single call to fdelay_config_pulse takes 2.1ms to complete). The time is spent in driving the GPIO enable line that controls the output stage decoupling. This is done via SPI, and each spi_xfer takes 420us, which add up to the reported delay. The fix leaves the enable pins always on, so the output relay is not used to control whether the outputs are enabled/disabled; it is the DCR enable bit who takes this role instead. This results in an average 8us time for output delay configuration, 3us for output disable. Conflicts: kernel/fd-zio.c
23d5e85c · Juan David González Cobas · ced80103 · 23d5e85c · 23d5e85c
Commit 23d5e85c authored Jun 13, 2013 by Juan David González Cobas
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Showing with 11 additions and 7 deletions

fd-core.c kernel/fd-core.c +5 -1

fd-zio.c kernel/fd-zio.c +6 -6

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--- a/kernel/fd-core.c
+++ b/kernel/fd-core.c
@@ -129,7 +129,7 @@ int fd_probe(struct fmc_device *fmc)
 	struct fd_dev *fd;
 	struct device *dev = &fmc->dev;
 	char *fwname;
-	int i, index, ret;
+	int i, index, ret, ch;

 	fd = kzalloc(sizeof(*fd), GFP_KERNEL);
 	if (!fd) {
@@ -258,6 +258,10 @@ int fd_probe(struct fmc_device *fmc)
 		       ts3.tv_sec, ts3.tv_nsec);
 	}
 	set_bit(FD_FLAG_INITED, &fd->flags);
+
+	/* set all output enable stages */
+	for (ch = 1; ch <= FD_CH_NUMBER; ch++)
+		fd_gpio_set(fd, FD_GPIO_OUTPUT_EN(ch));
 	return 0;

 err:

--- a/kernel/fd-zio.c
+++ b/kernel/fd-zio.c
@@ -435,7 +435,9 @@ static void __fd_zio_output(struct fd_dev *fd, int index1_4, uint32_t *attrs)
 	int dcr;

 	if (mode == FD_OUT_MODE_DISABLED) {
-		fd_gpio_clr(fd, FD_GPIO_OUTPUT_EN(index1_4));
+		/* disable output via DCR register */
+		dcr = 0;
+		fd_ch_writel(fd, ch, dcr, FD_REG_DCR);
 		return;
 	}

@@ -538,11 +540,9 @@ static void __fd_zio_output(struct fd_dev *fd, int index1_4, uint32_t *attrs)
 	fd_ch_writel(fd, ch, dcr, FD_REG_DCR);
 	fd_ch_writel(fd, ch, dcr | FD_DCR_UPDATE, FD_REG_DCR);
 	fd_ch_writel(fd, ch, dcr | FD_DCR_ENABLE, FD_REG_DCR);
-	if (mode == FD_OUT_MODE_PULSE)
-		fd_ch_writel(fd, ch, dcr | FD_DCR_ENABLE | FD_DCR_PG_ARM,
-			     FD_REG_DCR);
-
-	fd_gpio_set(fd, FD_GPIO_OUTPUT_EN(index1_4));
+	if (mode == FD_OUT_MODE_PULSE) {
+		fd_ch_writel(fd, ch, dcr | FD_DCR_ENABLE | FD_DCR_PG_ARM,  FD_REG_DCR);
+	}
 }

 /* This is called on user write */