Hi Tomi,
Thank you for the patch.
On Tuesday 28 Mar 2017 16:07:47 Tomi Valkeinen wrote:
> DRA7 errata i886 (FPDLink PLL Unlocks With Certain SoC PLL M/N Values)
> says that FPDLink is sensitive to jitter on the vout clock, and that low
> PLL M and N values result in more jitter than high M and N values.
>
> This patch implements a workaround for the problem by changing the PLL
> setup to search for clocks starting from high M and N values, instead of
> low values. This should not cause any functional change, and only
> reduces the jitter.
>
> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@xxxxxx>
Reviewed-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/omapdrm/dss/pll.c | 17 +++++++++--------
> 1 file changed, 9 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/omapdrm/dss/pll.c
> b/drivers/gpu/drm/omapdrm/dss/pll.c index 0a76c89cdc2e..5e221302768b 100644
> --- a/drivers/gpu/drm/omapdrm/dss/pll.c
> +++ b/drivers/gpu/drm/omapdrm/dss/pll.c
> @@ -215,8 +215,8 @@ bool dss_pll_calc_a(const struct dss_pll *pll, unsigned
> long clkin, dss_pll_calc_func func, void *data)
> {
> const struct dss_pll_hw *hw = pll->hw;
> - int n, n_start, n_stop;
> - int m, m_start, m_stop;
> + int n, n_min, n_max;
> + int m, m_min, m_max;
> unsigned long fint, clkdco;
> unsigned long pll_hw_max;
> unsigned long fint_hw_min, fint_hw_max;
> @@ -226,21 +226,22 @@ bool dss_pll_calc_a(const struct dss_pll *pll,
> unsigned long clkin, fint_hw_min = hw->fint_min;
> fint_hw_max = hw->fint_max;
>
> - n_start = max(DIV_ROUND_UP(clkin, fint_hw_max), 1ul);
> - n_stop = min((unsigned)(clkin / fint_hw_min), hw->n_max);
> + n_min = max(DIV_ROUND_UP(clkin, fint_hw_max), 1ul);
> + n_max = min((unsigned)(clkin / fint_hw_min), hw->n_max);
>
> pll_max = pll_max ? pll_max : ULONG_MAX;
>
> - for (n = n_start; n <= n_stop; ++n) {
> + /* Try to find high N & M to avoid jitter (DRA7 errata i886) */
> + for (n = n_max; n >= n_min; --n) {
> fint = clkin / n;
>
> - m_start = max(DIV_ROUND_UP(DIV_ROUND_UP(pll_min, fint), 2),
> + m_min = max(DIV_ROUND_UP(DIV_ROUND_UP(pll_min, fint), 2),
> 1ul);
> - m_stop = min3((unsigned)(pll_max / fint / 2),
> + m_max = min3((unsigned)(pll_max / fint / 2),
> (unsigned)(pll_hw_max / fint / 2),
> hw->m_max);
>
> - for (m = m_start; m <= m_stop; ++m) {
> + for (m = m_max; m >= m_min; --m) {
> clkdco = 2 * m * fint;
>
> if (func(n, m, fint, clkdco, data))
--
Regards,
Laurent Pinchart
_______________________________________________
dri-devel mailing list
dri-devel@xxxxxxxxxxxxxxxxxxxxx
https://lists.freedesktop.org/mailman/listinfo/dri-devel
