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    Subject[PATCH 3.12 82/83] drm/radeon/audio: improve ACR calculation
    Date
    3.12-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    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;
    }

    --
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