[PATCH v1 14/24] powerpc/mpc512x: improve DIU related clock setup
Gerhard Sittig
gsi at denx.de
Tue Jul 16 04:47:43 EST 2013
adapt the DIU clock initialization to the COMMON_CLK approach: device
tree based clock lookup, prepare and unprepare for clocks, work with
frequencies not dividers, call the appropriate clk_*() routines and
don't access CCM registers, remove the pre-enable workaround in the
platform's clock driver
the "best clock" determination now completely relies on the platform's
clock driver to pick a frequency close to what the caller requests, and
merely checks whether the desired frequency was met (is acceptable since
it meets the tolerance of the monitor) -- this approach shall succeed
upon first try in the usual case, will test a few less desirable yet
acceptable frequencies in edge cases, and will fallback to "best effort"
if none of the previously tried frequencies pass the test
Signed-off-by: Gerhard Sittig <gsi at denx.de>
---
arch/powerpc/platforms/512x/clock-commonclk.c | 1 -
arch/powerpc/platforms/512x/mpc512x_shared.c | 165 +++++++++++++------------
2 files changed, 88 insertions(+), 78 deletions(-)
diff --git a/arch/powerpc/platforms/512x/clock-commonclk.c b/arch/powerpc/platforms/512x/clock-commonclk.c
index 218f55b..f31f895 100644
--- a/arch/powerpc/platforms/512x/clock-commonclk.c
+++ b/arch/powerpc/platforms/512x/clock-commonclk.c
@@ -705,7 +705,6 @@ static void mpc512x_clk_setup_clock_tree(int busfreq)
/* some are not yet acquired by their respective drivers */
clk_prepare_enable(clks[MPC512x_CLK_PSC3_MCLK]);/* serial console */
clk_prepare_enable(clks[MPC512x_CLK_FEC]); /* network, NFS */
- clk_prepare_enable(clks[MPC512x_CLK_DIU]); /* display */
clk_prepare_enable(clks[MPC512x_CLK_I2C]);
/*
* some have their individual clock subtree with separate clock
diff --git a/arch/powerpc/platforms/512x/mpc512x_shared.c b/arch/powerpc/platforms/512x/mpc512x_shared.c
index a82a41b..3381eea 100644
--- a/arch/powerpc/platforms/512x/mpc512x_shared.c
+++ b/arch/powerpc/platforms/512x/mpc512x_shared.c
@@ -12,6 +12,7 @@
* (at your option) any later version.
*/
+#include <linux/clk.h>
#include <linux/kernel.h>
#include <linux/io.h>
#include <linux/irq.h>
@@ -70,98 +71,108 @@ struct fsl_diu_shared_fb {
bool in_use;
};
-#define DIU_DIV_MASK 0x000000ff
+/* receives a pixel clock spec in pico seconds, adjusts the DIU clock rate */
void mpc512x_set_pixel_clock(unsigned int pixclock)
{
- unsigned long bestval, bestfreq, speed, busfreq;
- unsigned long minpixclock, maxpixclock, pixval;
- struct mpc512x_ccm __iomem *ccm;
struct device_node *np;
- u32 temp;
- long err;
- int i;
+ struct clk *clk_diu;
+ unsigned long epsilon, minpixclock, maxpixclock;
+ unsigned long offset, want, got, delta;
- np = of_find_compatible_node(NULL, NULL, "fsl,mpc5121-clock");
+ /* lookup and enable the DIU clock */
+ np = of_find_compatible_node(NULL, NULL, "fsl,mpc5121-diu");
if (!np) {
- pr_err("Can't find clock control module.\n");
+ pr_err("Could not find DIU device tree node.\n");
return;
}
-
- ccm = of_iomap(np, 0);
+ clk_diu = of_clk_get_by_name(np, "per");
of_node_put(np);
- if (!ccm) {
- pr_err("Can't map clock control module reg.\n");
+ if (IS_ERR(clk_diu)) {
+ pr_err("Could not lookup DIU clock.\n");
return;
}
-
- np = of_find_node_by_type(NULL, "cpu");
- if (np) {
- const unsigned int *prop =
- of_get_property(np, "bus-frequency", NULL);
-
- of_node_put(np);
- if (prop) {
- busfreq = *prop;
- } else {
- pr_err("Can't get bus-frequency property\n");
- return;
- }
- } else {
- pr_err("Can't find 'cpu' node.\n");
+ if (clk_prepare_enable(clk_diu)) {
+ pr_err("Could not enable DIU clock.\n");
return;
}
- /* Pixel Clock configuration */
- pr_debug("DIU: Bus Frequency = %lu\n", busfreq);
- speed = busfreq * 4; /* DIU_DIV ratio is 4 * CSB_CLK / DIU_CLK */
-
- /* Calculate the pixel clock with the smallest error */
- /* calculate the following in steps to avoid overflow */
- pr_debug("DIU pixclock in ps - %d\n", pixclock);
- temp = (1000000000 / pixclock) * 1000;
- pixclock = temp;
- pr_debug("DIU pixclock freq - %u\n", pixclock);
-
- temp = temp / 20; /* pixclock * 0.05 */
- pr_debug("deviation = %d\n", temp);
- minpixclock = pixclock - temp;
- maxpixclock = pixclock + temp;
- pr_debug("DIU minpixclock - %lu\n", minpixclock);
- pr_debug("DIU maxpixclock - %lu\n", maxpixclock);
- pixval = speed/pixclock;
- pr_debug("DIU pixval = %lu\n", pixval);
-
- err = LONG_MAX;
- bestval = pixval;
- pr_debug("DIU bestval = %lu\n", bestval);
-
- bestfreq = 0;
- for (i = -1; i <= 1; i++) {
- temp = speed / (pixval+i);
- pr_debug("DIU test pixval i=%d, pixval=%lu, temp freq. = %u\n",
- i, pixval, temp);
- if ((temp < minpixclock) || (temp > maxpixclock))
- pr_debug("DIU exceeds monitor range (%lu to %lu)\n",
- minpixclock, maxpixclock);
- else if (abs(temp - pixclock) < err) {
- pr_debug("Entered the else if block %d\n", i);
- err = abs(temp - pixclock);
- bestval = pixval + i;
- bestfreq = temp;
- }
+ /*
+ * convert the picoseconds spec into the desired clock rate,
+ * determine the acceptable clock range for the monitor (+/- 5%),
+ * do the calculation in steps to avoid integer overflow
+ */
+ pr_debug("DIU pixclock in ps - %u\n", pixclock);
+ pixclock = (1000000000 / pixclock) * 1000;
+ pr_debug("DIU pixclock freq - %u\n", pixclock);
+ epsilon = pixclock / 20; /* pixclock * 0.05 */
+ pr_debug("DIU deviation - %lu\n", epsilon);
+ minpixclock = pixclock - epsilon;
+ maxpixclock = pixclock + epsilon;
+ pr_debug("DIU minpixclock - %lu\n", minpixclock);
+ pr_debug("DIU maxpixclock - %lu\n", maxpixclock);
+
+ /*
+ * check whether the DIU supports the desired pixel clock
+ *
+ * - simply request the desired clock and see what the
+ * platform's clock driver will make of it, assuming that it
+ * will setup the best approximation of the requested value
+ * - try other candidate frequencies in the order of decreasing
+ * preference (i.e. with increasing distance from the desired
+ * pixel clock, and checking the lower frequency before the
+ * higher frequency to not overload the hardware) until the
+ * first match is found -- any potential subsequent match
+ * would only be as good as the former match or typically
+ * would be less preferrable
+ *
+ * the offset increment of pixelclock divided by 64 is an
+ * arbitrary choice -- it's simple to calculate, in the typical
+ * case we expect the first check to succeed already, in the
+ * worst case seven frequencies get tested (the exact center and
+ * three more values each to the left and to the right) before
+ * the 5% tolerance window is exceeded, resulting in fast enough
+ * execution yet high enough probability of finding a suitable
+ * value, while the error rate will be in the order of single
+ * percents
+ */
+ for (offset = 0; offset <= epsilon; offset += pixclock / 64) {
+ want = pixclock - offset;
+ pr_debug("DIU checking clock - %lu\n", want);
+ clk_set_rate(clk_diu, want);
+ got = clk_get_rate(clk_diu);
+ delta = abs(pixclock - got);
+ if (delta < epsilon)
+ break;
+ if (!offset)
+ continue;
+ want = pixclock + offset;
+ pr_debug("DIU checking clock - %lu\n", want);
+ clk_set_rate(clk_diu, want);
+ got = clk_get_rate(clk_diu);
+ delta = abs(pixclock - got);
+ if (delta < epsilon)
+ break;
}
+ if (offset <= epsilon) {
+ pr_debug("DIU clock accepted - %lu\n", want);
+ pr_debug("DIU pixclock want %u, got %lu, delta %lu, eps %lu\n",
+ pixclock, got, delta, epsilon);
+ return;
+ }
+ pr_warn("DIU pixclock auto search unsuccessful\n");
- pr_debug("DIU chose = %lx\n", bestval);
- pr_debug("DIU error = %ld\n NomPixClk ", err);
- pr_debug("DIU: Best Freq = %lx\n", bestfreq);
- /* Modify DIU_DIV in CCM SCFR1 */
- temp = in_be32(&ccm->scfr1);
- pr_debug("DIU: Current value of SCFR1: 0x%08x\n", temp);
- temp &= ~DIU_DIV_MASK;
- temp |= (bestval & DIU_DIV_MASK);
- out_be32(&ccm->scfr1, temp);
- pr_debug("DIU: Modified value of SCFR1: 0x%08x\n", temp);
- iounmap(ccm);
+ /*
+ * what is the most appropriate action to take when the search
+ * for an available pixel clock which is acceptable to the
+ * monitor has failed? disable the DIU (clock) or just provide
+ * a "best effort"? we go with the latter
+ */
+ pr_warn("DIU pixclock best effort fallback (backend's choice)\n");
+ clk_set_rate(clk_diu, pixclock);
+ got = clk_get_rate(clk_diu);
+ delta = abs(pixclock - got);
+ pr_debug("DIU pixclock want %u, got %lu, delta %lu, eps %lu\n",
+ pixclock, got, delta, epsilon);
}
enum fsl_diu_monitor_port
--
1.7.10.4
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