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drm/radeon/audio: improve ACR calculation 

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>
This commit is contained in:
Pierre Ossman 2013-11-06 20:09:08 +01:00 committed by Alex Deucher
parent 3e71985f24
commit a2098250fb
1 changed files with 48 additions and 24 deletions
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72
drivers/gpu/drm/radeon/r600_hdmi.c
View File

@ -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_hdmi_predefined_acr[] = {
{ 74250, 4096, 74250, 6272, 82500, 6144, 74250 }, /* 74.25 MHz */
{ 148352, 4096, 148352, 5733, 150670, 6144, 148352 }, /* 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
*/
static void r600_hdmi_calc_cts(uint32_t clock, int *CTS, int N, int freq)
{
u64 n;
u32 d;
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);
/*
* 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)
{
int n, cts;
unsigned long div, mul;
/* 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(uint32_t clock)
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];
/* 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];
}
/* 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);
/* 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;
}