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Message-ID: <20170919180025.apb4aq7ca3filh6c@art_vandelay>
Date: Tue, 19 Sep 2017 11:00:25 -0700
From: Sean Paul <seanpaul@...omium.org>
To: Nickey Yang <nickey.yang@...k-chips.com>
Cc: mark.yao@...k-chips.com, robh+dt@...nel.org, heiko@...ech.de,
mark.rutland@....com, airlied@...ux.ie,
linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
linux-rockchip@...ts.infradead.org, seanpaul@...omium.org,
briannorris@...omium.org, hl@...k-chips.com, zyw@...k-chips.com,
bivvy.bi@...k-chips.com, xbl@...k-chips.com
Subject: Re: [PATCH 1/7] drm/rockchip/dsi: correct Feedback divider setting
On Mon, Sep 18, 2017 at 05:05:33PM +0800, Nickey Yang wrote:
> This patch correct Feedback divider setting:
> 1、Set Feedback divider [8:5] when HIGH_PROGRAM_EN
> 2、Due to the use of a "by 2 pre-scaler," the range of the
> feedback multiplication Feedback divider is limited to even
> division numbers, and Feedback divider must be greater than
> 12, less than 1000.
> 3、Make the previously configured Feedback divider(LSB)
> factors effective
>
> Signed-off-by: Nickey Yang <nickey.yang@...k-chips.com>
> ---
> drivers/gpu/drm/rockchip/dw-mipi-dsi.c | 83 ++++++++++++++++++++++------------
> 1 file changed, 54 insertions(+), 29 deletions(-)
>
> diff --git a/drivers/gpu/drm/rockchip/dw-mipi-dsi.c b/drivers/gpu/drm/rockchip/dw-mipi-dsi.c
> index 9a20b9d..52698b7 100644
> --- a/drivers/gpu/drm/rockchip/dw-mipi-dsi.c
> +++ b/drivers/gpu/drm/rockchip/dw-mipi-dsi.c
> @@ -228,7 +228,7 @@
> #define LOW_PROGRAM_EN 0
> #define HIGH_PROGRAM_EN BIT(7)
> #define LOOP_DIV_LOW_SEL(val) (((val) - 1) & 0x1f)
> -#define LOOP_DIV_HIGH_SEL(val) ((((val) - 1) >> 5) & 0x1f)
> +#define LOOP_DIV_HIGH_SEL(val) ((((val) - 1) >> 5) & 0xf)
> #define PLL_LOOP_DIV_EN BIT(5)
> #define PLL_INPUT_DIV_EN BIT(4)
>
> @@ -461,6 +461,7 @@ static int dw_mipi_dsi_phy_init(struct dw_mipi_dsi *dsi)
> dw_mipi_dsi_phy_write(dsi, 0x17, INPUT_DIVIDER(dsi->input_div));
> dw_mipi_dsi_phy_write(dsi, 0x18, LOOP_DIV_LOW_SEL(dsi->feedback_div) |
> LOW_PROGRAM_EN);
> + dw_mipi_dsi_phy_write(dsi, 0x19, PLL_LOOP_DIV_EN | PLL_INPUT_DIV_EN);
You do the same write 2 lines down. Are both needed? It would be nice if the
register names were also defined, so this is easier to read.
> dw_mipi_dsi_phy_write(dsi, 0x18, LOOP_DIV_HIGH_SEL(dsi->feedback_div) |
> HIGH_PROGRAM_EN);
> dw_mipi_dsi_phy_write(dsi, 0x19, PLL_LOOP_DIV_EN | PLL_INPUT_DIV_EN);
> @@ -521,11 +522,16 @@ static int dw_mipi_dsi_phy_init(struct dw_mipi_dsi *dsi)
> static int dw_mipi_dsi_get_lane_bps(struct dw_mipi_dsi *dsi,
> struct drm_display_mode *mode)
> {
> - unsigned int i, pre;
> - unsigned long mpclk, pllref, tmp;
> - unsigned int m = 1, n = 1, target_mbps = 1000;
> + unsigned long mpclk, tmp;
> + unsigned int target_mbps = 1000;
> unsigned int max_mbps = dptdin_map[ARRAY_SIZE(dptdin_map) - 1].max_mbps;
> int bpp;
> + unsigned long best_freq = 0;
> + unsigned long fvco_min, fvco_max, fin ,fout;
> + unsigned int min_prediv, max_prediv;
> + unsigned int _prediv, uninitialized_var(best_prediv);
> + unsigned long _fbdiv, uninitialized_var(best_fbdiv);
> + unsigned long min_delta = UINT_MAX;
Once you explicitly type these, make sure you use the appropriate _MAX value
(ie: U64_MAX)
>
> bpp = mipi_dsi_pixel_format_to_bpp(dsi->format);
> if (bpp < 0) {
> @@ -544,34 +550,53 @@ static int dw_mipi_dsi_get_lane_bps(struct dw_mipi_dsi *dsi,
> dev_err(dsi->dev, "DPHY clock frequency is out of range\n");
> }
>
> - pllref = DIV_ROUND_UP(clk_get_rate(dsi->pllref_clk), USEC_PER_SEC);
> - tmp = pllref;
> -
> - /*
> - * The limits on the PLL divisor are:
> - *
> - * 5MHz <= (pllref / n) <= 40MHz
> - *
> - * we walk over these values in descreasing order so that if we hit
> - * an exact match for target_mbps it is more likely that "m" will be
> - * even.
> - *
> - * TODO: ensure that "m" is even after this loop.
> - */
> - for (i = pllref / 5; i > (pllref / 40); i--) {
> - pre = pllref / i;
> - if ((tmp > (target_mbps % pre)) && (target_mbps / pre < 512)) {
> - tmp = target_mbps % pre;
> - n = i;
> - m = target_mbps / pre;
> + fin = clk_get_rate(dsi->pllref_clk);
> + fout = target_mbps * USEC_PER_SEC;
> +
> + /* constraint: 5Mhz < Fref / N < 40MHz */
> + min_prediv = DIV_ROUND_UP(fin, 40 * USEC_PER_SEC);
> + max_prediv = fin / (5 * USEC_PER_SEC);
> +
> + /* constraint: 80MHz < Fvco < 1500Mhz */
> + fvco_min = 80 * USEC_PER_SEC;
> + fvco_max = 1500 * USEC_PER_SEC;
> +
> + for (_prediv = min_prediv; _prediv <= max_prediv; _prediv++) {
> + u32 delta;
> + /* Fvco = Fref * M / N */
> + tmp = fout * _prediv;
> + do_div(tmp, fin);
> + _fbdiv = tmp;
Why use tmp at all? Can't you just use _fbdiv directly in do_div?
> + /*
> + * Due to the use of a "by 2 pre-scaler," the range of the
> + * feedback multiplication value M is limited to even division
> + * numbers, and m must be greater than 12, less than 1000.
> + */
> + if (_fbdiv < 12 || _fbdiv > 1000)
> + continue;
> +
> + if (_fbdiv % 2)
> + ++_fbdiv;
You can reduce this down to:
_fbdiv += _fbdiv % 2;
> +
> + tmp = (u64)_fbdiv * fin;
I'll echo Brian's concerns on type mixing here. Please be explicit with size
when you declare your variables.
> + do_div(tmp, _prediv);
> + if (tmp < fvco_min || tmp > fvco_max)
> + continue;
> +
> + delta = abs(fout - tmp);
> + if (delta < min_delta) {
> + best_prediv = _prediv;
> + best_fbdiv = _fbdiv;
> + min_delta = delta;
> + best_freq = tmp;
> }
> - if (tmp == 0)
> - break;
> }
>
> - dsi->lane_mbps = pllref / n * m;
> - dsi->input_div = n;
> - dsi->feedback_div = m;
> + if (best_freq) {
Should you return an error or log something if best_freq is not found?
> + dsi->lane_mbps = DIV_ROUND_UP(best_freq, USEC_PER_SEC);
> + dsi->input_div = best_prediv;
> + dsi->feedback_div = best_fbdiv;
> + }
>
> return 0;
> }
> --
> 1.9.1
>
>
--
Sean Paul, Software Engineer, Google / Chromium OS
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