Re: [PATCH v6 3/3] drm/rockchip: Add ROCKCHIP DW MIPI DSI controller driver

Brian Norris
2017-12-06T22:01:05Z

Hi Nickey, others,

I just want to highlight a thing or two here. Otherwise, my
'Reviewed-by' still basically stands (FWIW).

On Wed, Dec 06, 2017 at 05:08:21PM +0800, Nickey Yang wrote:
> Add the ROCKCHIP DSI controller driver that uses the Synopsys DesignWare
> MIPI DSI host controller bridge.
>
> Signed-off-by: Nickey Yang <nickey.yang@rock-chips.com>
> Signed-off-by: Brian Norris <briannorris@chromium.org>
> Reviewed-by: Brian Norris <briannorris@chromium.org>
> Reviewed-by: Sean Paul <seanpaul@chromium.org>
> ---
> change:
>
> v2:
> add err_pllref, remove unnecessary encoder.enable & disable
> correct spelling mistakes
> v3:
> call dw_mipi_dsi_unbind() in dw_mipi_dsi_rockchip_unbind()
> fix typo, use of_device_get_match_data(),
> change some ‘bind()’ logic into 'probe()'
> add 'dev_set_drvdata()'
> v4:
> return -EINVAL when can not get best_freq
> add a clarifying comment when get vco
> add review tag
> v5:
> keep our power domain enabled while touching GRF
> v6:
> change func dw_mipi_encoder_disable name to
> dw_mipi_dsi_encoder_disable

We noticed a regression w.r.t. pm_runtime_*() handling using this patch,
hence the pm_runtime changes in v5/v6. We actually need to keep our
power domain enabled in the mode_set() function, where we start to
configure some Rockchip-specific registers (GRF). More on that below.

>
> drivers/gpu/drm/rockchip/Kconfig | 2 +-
> drivers/gpu/drm/rockchip/Makefile | 2 +-
> drivers/gpu/drm/rockchip/dw-mipi-dsi.c | 1349 -----------------------
> drivers/gpu/drm/rockchip/dw-mipi-dsi_rockchip.c | 785 +++++++++++++
> drivers/gpu/drm/rockchip/rockchip_drm_drv.c | 2 +-
> drivers/gpu/drm/rockchip/rockchip_drm_drv.h | 2 +-
> 6 files changed, 789 insertions(+), 1353 deletions(-)
> delete mode 100644 drivers/gpu/drm/rockchip/dw-mipi-dsi.c
> create mode 100644 drivers/gpu/drm/rockchip/dw-mipi-dsi_rockchip.c
>

...

> diff --git a/drivers/gpu/drm/rockchip/dw-mipi-dsi_rockchip.c b/drivers/gpu/drm/rockchip/dw-mipi-dsi_rockchip.c
> new file mode 100644
> index 0000000..66ab6fe
> --- /dev/null
> +++ b/drivers/gpu/drm/rockchip/dw-mipi-dsi_rockchip.c
> @@ -0,0 +1,785 @@

...

> +static void dw_mipi_dsi_encoder_mode_set(struct drm_encoder *encoder,
> + struct drm_display_mode *mode,
> + struct drm_display_mode *adjusted)
> +{
> + struct dw_mipi_dsi_rockchip *dsi = to_dsi(encoder);
> + const struct rockchip_dw_dsi_chip_data *cdata = dsi->cdata;
> + int val, ret, mux;
> +
> + mux = drm_of_encoder_active_endpoint_id(dsi->dev->of_node,
> + &dsi->encoder);
> + if (mux < 0)
> + return;
> + /*
> + * For the RK3399, the clk of grf must be enabled before writing grf
> + * register. And for RK3288 or other soc, this grf_clk must be NULL,
> + * the clk_prepare_enable return true directly.
> + */
> + ret = clk_prepare_enable(dsi->grf_clk);
> + if (ret) {
> + DRM_DEV_ERROR(dsi->dev, "Failed to enable grf_clk: %d\n", ret);
> + return;
> + }
> + pm_runtime_get_sync(dsi->dev);

What happens if there's a clk_prepare_enable() failure or failure to
retrieve the endpoint ID earlier in this function? You won't call
pm_runtime_get_*()...but might we still see a call to
dw_mipi_dsi_encoder_disable(), which would mean we get unbalanced
runtime PM status?

Also (and more importantly), is it fair to do all of this in mode_set()?
I believe Archit asked about this before, and the reason we're doing
this stuff in mode_set() now (where previously, the Rockchip driver was
doing it in ->enable()) is because when Philippe extracted the synopsys
bridge driver, that code migrated to ->mode_set().

But, I'm reading the comments on drm_encoder_helper_funcs::mode_set, and
I see:

/**
* @mode_set:
*
* This callback is used to update the display mode of an encoder.
*
* Note that the display pipe is completely off when this function is
* called. Drivers which need hardware to be running before they program
* the new display mode (because they implement runtime PM) should not
* use this hook, because the helper library calls it only once and not
* every time the display pipeline is suspend using either DPMS or the
* new "ACTIVE" property. Such drivers should instead move all their
* encoder setup into the @enable callback.

That sounds like perhaps the synopsys driver should be moving to use
->enable() instead, so the Rockchip driver can do that as well?

At any rate, I haven't found any real problem with using mode_set() so
far, but I was just curious what the recommended practice was.

> + val = cdata->dsi0_en_bit << 16;
> + if (mux)
> + val |= cdata->dsi0_en_bit;
> + regmap_write(dsi->grf_regmap, cdata->grf_switch_reg, val);
> +
> + if (cdata->grf_dsi0_mode_reg)
> + regmap_write(dsi->grf_regmap, cdata->grf_dsi0_mode_reg,
> + cdata->grf_dsi0_mode);
> +
> + clk_disable_unprepare(dsi->grf_clk);
> +}
> +
> +static int
> +dw_mipi_dsi_encoder_atomic_check(struct drm_encoder *encoder,
> + struct drm_crtc_state *crtc_state,
> + struct drm_connector_state *conn_state)
> +{
> + struct rockchip_crtc_state *s = to_rockchip_crtc_state(crtc_state);
> + struct dw_mipi_dsi_rockchip *dsi = to_dsi(encoder);
> +
> + switch (dsi->format) {
> + case MIPI_DSI_FMT_RGB888:
> + s->output_mode = ROCKCHIP_OUT_MODE_P888;
> + break;
> + case MIPI_DSI_FMT_RGB666:
> + s->output_mode = ROCKCHIP_OUT_MODE_P666;
> + break;
> + case MIPI_DSI_FMT_RGB565:
> + s->output_mode = ROCKCHIP_OUT_MODE_P565;
> + break;
> + default:
> + WARN_ON(1);
> + return -EINVAL;
> + }
> +
> + s->output_type = DRM_MODE_CONNECTOR_DSI;
> +
> + return 0;
> +}
> +
> +static void dw_mipi_dsi_encoder_disable(struct drm_encoder *encoder)
> +{
> + struct dw_mipi_dsi_rockchip *dsi = to_dsi(encoder);
> +
> + pm_runtime_put(dsi->dev);
> +}
> +
> +static const struct drm_encoder_helper_funcs
> +dw_mipi_dsi_encoder_helper_funcs = {
> + .mode_set = dw_mipi_dsi_encoder_mode_set,
> + .atomic_check = dw_mipi_dsi_encoder_atomic_check,
> + .disable = dw_mipi_dsi_encoder_disable,
> +};

...

Brian