Date:   Thu, 7 Dec 2017 14:29:43 +0000
From:   Philippe CORNU <philippe.cornu@...com>
To:     Brian Norris <briannorris@...omium.org>,
        Nickey Yang <nickey.yang@...k-chips.com>
CC:     "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "heiko@...ech.de" <heiko@...ech.de>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "airlied@...ux.ie" <airlied@...ux.ie>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-rockchip@...ts.infradead.org" 
        <linux-rockchip@...ts.infradead.org>,
        "laurent.pinchart@...asonboard.com" 
        <laurent.pinchart@...asonboard.com>,
        "seanpaul@...omium.org" <seanpaul@...omium.org>,
        "mka@...omium.org" <mka@...omium.org>,
        "hoegsberg@...il.com" <hoegsberg@...il.com>,
        "architt@...eaurora.org" <architt@...eaurora.org>,
        Yannick FERTRE <yannick.fertre@...com>,
        "hl@...k-chips.com" <hl@...k-chips.com>,
        "zyw@...k-chips.com" <zyw@...k-chips.com>,
        "xbl@...k-chips.com" <xbl@...k-chips.com>
Subject: Re: [PATCH v6 3/3] drm/rockchip: Add ROCKCHIP DW MIPI DSI controller
 driver

Hi Brian,


On 12/06/2017 10:52 PM, Brian Norris wrote:
> 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@...k-chips.com>
>> Signed-off-by: Brian Norris <briannorris@...omium.org>
>> Reviewed-by: Brian Norris <briannorris@...omium.org>
>> Reviewed-by: Sean Paul <seanpaul@...omium.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().

Regarding mode_set(), let's me explain more what I did:
- transform the original code from Rockchip (encoder + connector drm 
api) to a generic bridge (bridge drm api).
- add panel-bridge interface
- ... (more details in the change log 
https://www.spinics.net/lists/dri-devel/msg147167.html)

So we have:
crtc -> dw mipi dsi bridge -> panel-bridge "bridge next" -> panel

The bridge pre_enable() calls first the "bridge next" pre_enable() (ie 
the panel-bridge pre-enable) before calling the bridge pre_enable (ie 
the dw mipi dsi bridge pre-enable (not used here). see in 
drm_bridge_pre_enable() in drm_bridge.c for details

The panel-bridge pre_enable() calls drm_panel_prepare(). See in 
bridge/panel.c for details.

So in the dw mipi dsi bridge, we need to configure and start 
"everything" before the bridge pre_enable so I put the "former" encoder 
enable() source code into the new bridge mode_set().

Tell me if I am not clear enough as it is not so easy to explain : )

Thanks,
Philippe :-)

> 
> 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
> 

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