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Message-ID: <CAPY8ntAuc4ySQBH7Q8MMhY3a0LkVp01nuWf-bCja53PMQ=0KVA@mail.gmail.com>
Date: Tue, 28 Jul 2020 15:56:53 +0100
From: Dave Stevenson <dave.stevenson@...pberrypi.com>
To: Maxime Ripard <maxime@...no.tech>
Cc: Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
Eric Anholt <eric@...olt.net>,
DRI Development <dri-devel@...ts.freedesktop.org>,
linux-rpi-kernel@...ts.infradead.org,
bcm-kernel-feedback-list@...adcom.com,
linux-arm-kernel@...ts.infradead.org,
LKML <linux-kernel@...r.kernel.org>,
Tim Gover <tim.gover@...pberrypi.com>,
Phil Elwell <phil@...pberrypi.com>
Subject: Re: [PATCH v4 62/78] drm/vc4: hdmi: Adjust HSM clock rate depending
on pixel rate
Hi Maxime
On Wed, 8 Jul 2020 at 18:44, Maxime Ripard <maxime@...no.tech> wrote:
>
> The HSM clock needs to be setup at around 101% of the pixel rate. This
> was done previously by setting the clock rate to 163.7MHz at probe time and
> only check in mode_valid whether the mode pixel clock was under the pixel
> clock +1% or not.
>
> However, with 4k we need to change that frequency to a higher frequency
> than 163.7MHz, and yet want to have the lowest clock as possible to have a
> decent power saving.
>
> Let's change that logic a bit by setting the clock rate of the HSM clock
> to the pixel rate at encoder_enable time. This would work for the
> BCM2711 that support 4k resolutions and has a clock that can provide it,
> but we still have to take care of a 4k panel plugged on a BCM283x SoCs
> that wouldn't be able to use those modes, so let's define the limit in
> the variant.
>
> Signed-off-by: Maxime Ripard <maxime@...no.tech>
Reviewed-by: Dave Stevenson <dave.stevenson@...pberrypi.com>
> ---
> drivers/gpu/drm/vc4/vc4_hdmi.c | 79 ++++++++++++++++-------------------
> drivers/gpu/drm/vc4/vc4_hdmi.h | 3 +-
> 2 files changed, 41 insertions(+), 41 deletions(-)
>
> diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
> index 17797b14cde4..9f30fab744f2 100644
> --- a/drivers/gpu/drm/vc4/vc4_hdmi.c
> +++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
> @@ -53,7 +53,6 @@
> #include "vc4_hdmi_regs.h"
> #include "vc4_regs.h"
>
> -#define HSM_CLOCK_FREQ 163682864
> #define CEC_CLOCK_FREQ 40000
>
> static int vc4_hdmi_debugfs_regs(struct seq_file *m, void *unused)
> @@ -326,6 +325,7 @@ static void vc4_hdmi_encoder_disable(struct drm_encoder *encoder)
> HDMI_WRITE(HDMI_VID_CTL,
> HDMI_READ(HDMI_VID_CTL) & ~VC4_HD_VID_CTL_ENABLE);
>
> + clk_disable_unprepare(vc4_hdmi->hsm_clock);
> clk_disable_unprepare(vc4_hdmi->pixel_clock);
>
> ret = pm_runtime_put(&vc4_hdmi->pdev->dev);
> @@ -423,6 +423,7 @@ static void vc4_hdmi_encoder_enable(struct drm_encoder *encoder)
> struct vc4_hdmi *vc4_hdmi = encoder_to_vc4_hdmi(encoder);
> struct vc4_hdmi_encoder *vc4_encoder = to_vc4_hdmi_encoder(encoder);
> bool debug_dump_regs = false;
> + unsigned long pixel_rate, hsm_rate;
> int ret;
>
> ret = pm_runtime_get_sync(&vc4_hdmi->pdev->dev);
> @@ -431,9 +432,8 @@ static void vc4_hdmi_encoder_enable(struct drm_encoder *encoder)
> return;
> }
>
> - ret = clk_set_rate(vc4_hdmi->pixel_clock,
> - mode->clock * 1000 *
> - ((mode->flags & DRM_MODE_FLAG_DBLCLK) ? 2 : 1));
> + pixel_rate = mode->clock * 1000 * ((mode->flags & DRM_MODE_FLAG_DBLCLK) ? 2 : 1);
> + ret = clk_set_rate(vc4_hdmi->pixel_clock, pixel_rate);
> if (ret) {
> DRM_ERROR("Failed to set pixel clock rate: %d\n", ret);
> return;
> @@ -445,6 +445,36 @@ static void vc4_hdmi_encoder_enable(struct drm_encoder *encoder)
> return;
> }
>
> + /*
> + * As stated in RPi's vc4 firmware "HDMI state machine (HSM) clock must
> + * be faster than pixel clock, infinitesimally faster, tested in
> + * simulation. Otherwise, exact value is unimportant for HDMI
> + * operation." This conflicts with bcm2835's vc4 documentation, which
> + * states HSM's clock has to be at least 108% of the pixel clock.
> + *
> + * Real life tests reveal that vc4's firmware statement holds up, and
> + * users are able to use pixel clocks closer to HSM's, namely for
> + * 1920x1200@...z. So it was decided to have leave a 1% margin between
> + * both clocks. Which, for RPi0-3 implies a maximum pixel clock of
> + * 162MHz.
> + *
> + * Additionally, the AXI clock needs to be at least 25% of
> + * pixel clock, but HSM ends up being the limiting factor.
> + */
> + hsm_rate = max_t(unsigned long, 120000000, (pixel_rate / 100) * 101);
> + ret = clk_set_rate(vc4_hdmi->hsm_clock, hsm_rate);
> + if (ret) {
> + DRM_ERROR("Failed to set HSM clock rate: %d\n", ret);
> + return;
> + }
> +
> + ret = clk_prepare_enable(vc4_hdmi->hsm_clock);
> + if (ret) {
> + DRM_ERROR("Failed to turn on HSM clock: %d\n", ret);
> + clk_disable_unprepare(vc4_hdmi->pixel_clock);
> + return;
> + }
> +
> if (vc4_hdmi->variant->reset)
> vc4_hdmi->variant->reset(vc4_hdmi);
>
> @@ -559,23 +589,9 @@ static enum drm_mode_status
> vc4_hdmi_encoder_mode_valid(struct drm_encoder *encoder,
> const struct drm_display_mode *mode)
> {
> - /*
> - * As stated in RPi's vc4 firmware "HDMI state machine (HSM) clock must
> - * be faster than pixel clock, infinitesimally faster, tested in
> - * simulation. Otherwise, exact value is unimportant for HDMI
> - * operation." This conflicts with bcm2835's vc4 documentation, which
> - * states HSM's clock has to be at least 108% of the pixel clock.
> - *
> - * Real life tests reveal that vc4's firmware statement holds up, and
> - * users are able to use pixel clocks closer to HSM's, namely for
> - * 1920x1200@...z. So it was decided to have leave a 1% margin between
> - * both clocks. Which, for RPi0-3 implies a maximum pixel clock of
> - * 162MHz.
> - *
> - * Additionally, the AXI clock needs to be at least 25% of
> - * pixel clock, but HSM ends up being the limiting factor.
> - */
> - if (mode->clock > HSM_CLOCK_FREQ / (1000 * 101 / 100))
> + struct vc4_hdmi *vc4_hdmi = encoder_to_vc4_hdmi(encoder);
> +
> + if ((mode->clock * 1000) > vc4_hdmi->variant->max_pixel_clock)
> return MODE_CLOCK_HIGH;
>
> return MODE_OK;
> @@ -1349,23 +1365,6 @@ static int vc4_hdmi_bind(struct device *dev, struct device *master, void *data)
> return -EPROBE_DEFER;
> }
>
> - /* This is the rate that is set by the firmware. The number
> - * needs to be a bit higher than the pixel clock rate
> - * (generally 148.5Mhz).
> - */
> - ret = clk_set_rate(vc4_hdmi->hsm_clock, HSM_CLOCK_FREQ);
> - if (ret) {
> - DRM_ERROR("Failed to set HSM clock rate: %d\n", ret);
> - goto err_put_i2c;
> - }
> -
> - ret = clk_prepare_enable(vc4_hdmi->hsm_clock);
> - if (ret) {
> - DRM_ERROR("Failed to turn on HDMI state machine clock: %d\n",
> - ret);
> - goto err_put_i2c;
> - }
> -
> /* Only use the GPIO HPD pin if present in the DT, otherwise
> * we'll use the HDMI core's register.
> */
> @@ -1413,9 +1412,7 @@ static int vc4_hdmi_bind(struct device *dev, struct device *master, void *data)
> err_destroy_encoder:
> drm_encoder_cleanup(encoder);
> err_unprepare_hsm:
> - clk_disable_unprepare(vc4_hdmi->hsm_clock);
> pm_runtime_disable(dev);
> -err_put_i2c:
> put_device(&vc4_hdmi->ddc->dev);
>
> return ret;
> @@ -1454,7 +1451,6 @@ static void vc4_hdmi_unbind(struct device *dev, struct device *master,
> vc4_hdmi_connector_destroy(&vc4_hdmi->connector);
> drm_encoder_cleanup(&vc4_hdmi->encoder.base.base);
>
> - clk_disable_unprepare(vc4_hdmi->hsm_clock);
> pm_runtime_disable(dev);
>
> put_device(&vc4_hdmi->ddc->dev);
> @@ -1479,6 +1475,7 @@ static int vc4_hdmi_dev_remove(struct platform_device *pdev)
> static const struct vc4_hdmi_variant bcm2835_variant = {
> .encoder_type = VC4_ENCODER_TYPE_HDMI0,
> .debugfs_name = "hdmi_regs",
> + .max_pixel_clock = 162000000,
> .cec_available = true,
> .registers = vc4_hdmi_fields,
> .num_registers = ARRAY_SIZE(vc4_hdmi_fields),
> diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.h b/drivers/gpu/drm/vc4/vc4_hdmi.h
> index 3f07aebe89f1..342f6e0227a2 100644
> --- a/drivers/gpu/drm/vc4/vc4_hdmi.h
> +++ b/drivers/gpu/drm/vc4/vc4_hdmi.h
> @@ -36,6 +36,9 @@ struct vc4_hdmi_variant {
> /* Set to true when the CEC support is available */
> bool cec_available;
>
> + /* Maximum pixel clock supported by the controller (in Hz) */
> + unsigned long long max_pixel_clock;
> +
> /* List of the registers available on that variant */
> const struct vc4_hdmi_register *registers;
>
> --
> git-series 0.9.1
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