[PATCH 3.12 82/83] drm/radeon/audio: improve ACR calculation

Greg Kroah-Hartman
2013-12-06T21:53:33Z

From: Pierre Ossman <pierre@ossman.eu>

commit a2098250fbda149cfad9e626afe80abe3b21e574 upstream.

In order to have any realistic chance of calculating proper
ACR values, we need to be able to calculate both N and CTS,
not just CTS. We still aim for the ideal N as specified in
the HDMI spec though.

bug:
https://bugs.freedesktop.org/show_bug.cgi?id=69675

Signed-off-by: Pierre Ossman <pierre@ossman.eu>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: Josh Boyer <jwboyer@fedoraproject.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/gpu/drm/radeon/r600_hdmi.c | 68 +++++++++++++++++++++++++------------
1 file changed, 46 insertions(+), 22 deletions(-)

--- a/drivers/gpu/drm/radeon/r600_hdmi.c
+++ b/drivers/gpu/drm/radeon/r600_hdmi.c
@@ -24,6 +24,7 @@
* Authors: Christian König
*/
#include <linux/hdmi.h>
+#include <linux/gcd.h>
#include <drm/drmP.h>
#include <drm/radeon_drm.h>
#include "radeon.h"
@@ -67,25 +68,47 @@ static const struct radeon_hdmi_acr r600
{ 74250, 4096, 74250, 6272, 82500, 6144, 74250 }, /* 74.25 MHz */
{ 148352, 11648, 421875, 8918, 234375, 5824, 140625 }, /* 148.50/1.001 MHz */
{ 148500, 4096, 148500, 6272, 165000, 6144, 148500 }, /* 148.50 MHz */
- { 0, 4096, 0, 6272, 0, 6144, 0 } /* Other */
};

+
/*
- * calculate CTS value if it's not found in the table
+ * calculate CTS and N values if they are not found in the table
*/
-static void r600_hdmi_calc_cts(uint32_t clock, int *CTS, int N, int freq)
+static void r600_hdmi_calc_cts(uint32_t clock, int *CTS, int *N, int freq)
{
- u64 n;
- u32 d;
+ int n, cts;
+ unsigned long div, mul;

- if (*CTS == 0) {
- n = (u64)clock * (u64)N * 1000ULL;
- d = 128 * freq;
- do_div(n, d);
- *CTS = n;
- }
- DRM_DEBUG("Using ACR timing N=%d CTS=%d for frequency %d\n",
- N, *CTS, freq);
+ /* Safe, but overly large values */
+ n = 128 * freq;
+ cts = clock * 1000;
+
+ /* Smallest valid fraction */
+ div = gcd(n, cts);
+
+ n /= div;
+ cts /= div;
+
+ /*
+ * The optimal N is 128*freq/1000. Calculate the closest larger
+ * value that doesn't truncate any bits.
+ */
+ mul = ((128*freq/1000) + (n-1))/n;
+
+ n *= mul;
+ cts *= mul;
+
+ /* Check that we are in spec (not always possible) */
+ if (n < (128*freq/1500))
+ printk(KERN_WARNING "Calculated ACR N value is too small. You may experience audio problems.\n");
+ if (n > (128*freq/300))
+ printk(KERN_WARNING "Calculated ACR N value is too large. You may experience audio problems.\n");
+
+ *N = n;
+ *CTS = cts;
+
+ DRM_DEBUG("Calculated ACR timing N=%d CTS=%d for frequency %d\n",
+ *N, *CTS, freq);
}

struct radeon_hdmi_acr r600_hdmi_acr(uint32_t clock)
@@ -93,15 +116,16 @@ struct radeon_hdmi_acr r600_hdmi_acr(uin
struct radeon_hdmi_acr res;
u8 i;

- for (i = 0; r600_hdmi_predefined_acr[i].clock != clock &&
- r600_hdmi_predefined_acr[i].clock != 0; i++)
- ;
- res = r600_hdmi_predefined_acr[i];
-
- /* In case some CTS are missing */
- r600_hdmi_calc_cts(clock, &res.cts_32khz, res.n_32khz, 32000);
- r600_hdmi_calc_cts(clock, &res.cts_44_1khz, res.n_44_1khz, 44100);
- r600_hdmi_calc_cts(clock, &res.cts_48khz, res.n_48khz, 48000);
+ /* Precalculated values for common clocks */
+ for (i = 0; i < ARRAY_SIZE(r600_hdmi_predefined_acr); i++) {
+ if (r600_hdmi_predefined_acr[i].clock == clock)
+ return r600_hdmi_predefined_acr[i];
+ }
+
+ /* And odd clocks get manually calculated */
+ r600_hdmi_calc_cts(clock, &res.cts_32khz, &res.n_32khz, 32000);
+ r600_hdmi_calc_cts(clock, &res.cts_44_1khz, &res.n_44_1khz, 44100);
+ r600_hdmi_calc_cts(clock, &res.cts_48khz, &res.n_48khz, 48000);

return res;
}