Date:	Mon, 23 Mar 2015 16:33:26 +0530
From:	Archit Taneja <architt@...eaurora.org>
To:	hali@...eaurora.org
CC:	dri-devel@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] drm/msm: Initial add DSI connector support

Hi Hai,

On 03/19/2015 02:35 AM, hali@...eaurora.org wrote:
> Hi Archit,
>
> Thanks for your comments. Please see my response for some comments below.
> Comments without response will be addressed in patch version 2. I will
> wait for other comments if any to push patch V2.
>
>>> +static int dsi_gpio_init(struct msm_dsi_host *msm_host)
>>> +{
>>> +	int ret;
>>> +
>>> +	msm_host->disp_en_gpio = devm_gpiod_get(&msm_host->pdev->dev,
>>> +						"disp-enable");
>>> +	if (IS_ERR(msm_host->disp_en_gpio)) {
>>> +		pr_warn("%s: cannot get disp-enable-gpios %ld\n",
>>> +			__func__, PTR_ERR(msm_host->disp_en_gpio));
>>> +		msm_host->disp_en_gpio = NULL;
>>> +	}
>>> +	if (msm_host->disp_en_gpio) {
>>> +		ret = gpiod_direction_output(msm_host->disp_en_gpio, 0);
>>> +		if (ret) {
>>> +			pr_err("cannot set dir to disp-en-gpios %d\n", ret);
>>> +			return ret;
>>> +		}
>>> +	}
>>> +
>>> +	msm_host->te_gpio = devm_gpiod_get(&msm_host->pdev->dev, "disp-te");
>>> +	if (IS_ERR(msm_host->te_gpio)) {
>>> +		pr_warn("%s: cannot get disp-te-gpios %ld\n",
>>> +			__func__, PTR_ERR(msm_host->te_gpio));
>>
>> Video mode panels won't have te_gpio, we could probably make this
>> pr_debug()
>>
>>> +		msm_host->te_gpio = NULL;
>>> +	}
>>> +
>>> +	if (msm_host->te_gpio) {
>>> +		ret = gpiod_direction_input(msm_host->te_gpio);
>>> +		if (ret) {
>>> +			pr_err("%s: cannot set dir to disp-te-gpios, %d\n",
>>> +				__func__, ret);
>>> +			return ret;
>>> +		}
>>> +	}
>>
>> These gpios currently need to be declared under the dsi DT node. Even if
>> these are controlled via the dsi host, the gpios should still come under
>> the panel DT node.
>>
>> We shout get the panel's of_node here and look for these.
>>
>
>>> +static void dsi_sw_reset(struct msm_dsi_host *msm_host)
>>> +{
>>> +	dsi_write(msm_host, REG_DSI_CLK_CTRL,
>>> +		DSI_CLK_CTRL_AHBS_HCLK_ON | DSI_CLK_CTRL_AHBM_SCLK_ON |
>>> +		DSI_CLK_CTRL_PCLK_ON | DSI_CLK_CTRL_DSICLK_ON |
>>> +		DSI_CLK_CTRL_BYTECLK_ON | DSI_CLK_CTRL_ESCCLK_ON |
>>> +		DSI_CLK_CTRL_FORCE_ON_DYN_AHBM_HCLK);
>>
>> The same 7 bits seem to be set elsewhere, maybe make this a macro
>> DSI_ENABLE_CLKS or something similar?
>>
>
>>> +int msm_dsi_host_init(struct msm_dsi *msm_dsi)
>>> +{
>>> +	struct msm_dsi_host *msm_host = NULL;
>>> +	struct platform_device *pdev = msm_dsi->pdev;
>>> +	int ret = 0;
>>> +
>>> +	msm_host = devm_kzalloc(&pdev->dev, sizeof(*msm_host), GFP_KERNEL);
>>> +	if (!msm_host) {
>>> +		pr_err("%s: FAILED: cannot alloc dsi host\n",
>>> +		       __func__);
>>> +		ret = -ENOMEM;
>>> +		goto fail;
>>> +	}
>>> +
>>> +	ret = of_property_read_u32(pdev->dev.of_node,
>>> +				"cell-index", &msm_host->id);
>>
>> retrieving the instance number of a peripheral via a DT property like
>> 'cell-index' has been debated quite a bit in the past. I suppose it's
>> not the best thing to do.
>>
>> However, since the DSI instances in MDSS aren't completely identical(one
>> acts a master and other slave in dual dsi mode), maybe we can get away
>> with having a property like "qcom,dsi-master;", and that can be further
>> used to identify whether this node is DSI_0 or DSI_1
>>
>
> 2 DSIs are not always master-slave mode. It is possible that a single
> panel is connected to any of the hosts, or 2 panels are controlled
> independently. If 'cell-index' is not allowed to specify the instance
> number, i would prefer to have a simple property like
> "qcom,dsi-host-index".

Okay, thanks for that clarification.

>
>>> +int msm_dsi_host_register(struct mipi_dsi_host *host, bool check_defer)
>>> +{
>>> +	struct msm_dsi_host *msm_host = to_msm_dsi_host(host);
>>> +	struct device_node *node;
>>> +	int ret;
>>> +
>>> +	/* Register mipi dsi host */
>>> +	if (!msm_host->registered) {
>>> +		host->dev = &msm_host->pdev->dev;
>>> +		host->ops = &dsi_host_ops;
>>> +		ret = mipi_dsi_host_register(host);
>>> +		if (ret)
>>> +			return ret;
>>> +
>>> +		msm_host->registered = true;
>>> +
>>> +		/* If the panel driver has not been probed after host register,
>>> +		 * we should defer the host's probe.
>>> +		 * It makes sure panel is connected when fbcon detects
>>> +		 * connector status and gets the proper display mode to
>>> +		 * create framebuffer.
>>> +		 */
>>> +		if (check_defer) {
>>> +			node = of_parse_phandle(msm_host->pdev->dev.of_node,
>>> +						"qcom,panel", 0);
>>> +			if (node) {
>>> +				if (!of_drm_find_panel(node))
>>> +					return -EPROBE_DEFER;
>>> +			}
>>> +		}
>>> +	}
>>
>> We might have to defer probe multiple times before another dependency is
>> met. The above approach will let the driver defer only once without the
>> panel driver registered. During the second probe attempt, we'd just
>> return since 'msm_host->registered' would be true.
>>
>> I think we could move this check to end of dsi_init().
>>
>
> Once probe deferred, the private data structures will be cleaned up and
> re-allocated at the next probe. It should support multiple times probe
> deferral.

Ah right! I forgot about that. However, I don't think the panel would be 
a phandle entry under the dsi device node, right? Also, "qcom,panel" 
seems more like a compatible string to me. Should it rather be:

node = of_get_child_by_name(msm_host->pdev->dev.of_node, "panel");
if (node)
	...
	...

>
>>> +static int dsi_mgr_connector_mode_valid(struct drm_connector
>>> *connector,
>>> +				struct drm_display_mode *mode)
>>> +{
>>> +	int id = dsi_mgr_connector_get_id(connector);
>>> +	struct msm_dsi *msm_dsi = dsi_mgr_get_dsi(id);
>>> +	struct drm_encoder *encoder =
>>> +		(msm_dsi->panel_flags & MIPI_DSI_MODE_VIDEO) ?
>>> +		msm_dsi->base.encoders[MSM_DSI_VIDEO_ENCODER_ID] :
>>> +		msm_dsi->base.encoders[MSM_DSI_CMD_ENCODER_ID];
>>
>> Maybe you could make a helper 'msm_dsi_get_encoder(msm_dsi)' out of
>> this? It seems to be used elsewhere too.
>>
>
>>> +int msm_dsi_manager_register(struct msm_dsi *msm_dsi)
>>> +{
>>> +	struct msm_dsi_manager *msm_dsim = &msm_dsim_glb;
>>> +	int id = msm_dsi->id;
>>> +	struct msm_dsi *other_dsi = dsi_mgr_get_other_dsi(id);
>>> +	int ret;
>>> +
>>> +	if (id > DSI_MAX) {
>>> +		pr_err("%s: invalid id %d\n", __func__, id);
>>> +		return -EINVAL;
>>> +	}
>>> +
>>> +	if (msm_dsim->dsi[id]) {
>>> +		pr_err("%s: dsi%d already registered\n", __func__, id);
>>> +		return -EBUSY;
>>> +	}
>>> +
>>> +	msm_dsim->dsi[id] = msm_dsi;
>>> +
>>> +	ret = dsi_mgr_parse_dual_panel(msm_dsi->pdev->dev.of_node, id);
>>> +	if (ret) {
>>> +		pr_err("%s: failed to parse dual panel info\n", __func__);
>>> +		return ret;
>>> +	}
>>> +
>>> +	if (!IS_DUAL_PANEL()) {
>>> +		ret = msm_dsi_host_register(msm_dsi->host, true);
>>> +	} else if (!other_dsi) {
>>> +		return 0;
>>> +	} else {
>>> +		struct msm_dsi *mdsi = IS_MASTER_PANEL(id) ?
>>> +					msm_dsi : other_dsi;
>>> +		struct msm_dsi *sdsi = IS_MASTER_PANEL(id) ?
>>> +					other_dsi : msm_dsi;
>>> +		/* Register slave host first, so that slave DSI device
>>> +		 * has a chance to probe, and do not block the master
>>> +		 * DSI device's probe.
>>> +		 * Also, do not check defer for the slave host,
>>> +		 * because only master DSI device adds the panel to global
>>> +		 * panel list. The panel's device is the master DSI device.
>>> +		 */
>>> +		ret = msm_dsi_host_register(sdsi->host, false);
>>> +		if (ret)
>>> +			return ret;
>>> +		ret = msm_dsi_host_register(mdsi->host, true);
>>> +	}
>>> +
>>> +	return ret;
>>> +}
>>
>> The dual panel checks in these functions are quite intrusive at the
>> moment. We'd use DSI later where there won't be a panel at all. That
>> would result in ever more complicated checks.
>>
>> Is it possible to separate out the dual panel functionality such that it
>> becomes cleaner?
>>
>> For example msm_dsi_manager_phy_disable can look like:
>>
>> void msm_dsi_manager_phy_disable(int id)
>> {
>> 	...
>> 	...
>>
>> 	if (msm_dual_dsi_mode())
>> 		msm_dual_dsi_phy_disable(id);
>> 	else
>> 		msm_dsi_phy_disable(phy);
>>
>> 	...
>> }
>>
>> There might be repetition of some code between the normal and dual mode
>> case, but it will make things quite legible.
>>
>
> I think even we separate out the dual DSI functionality, we still need to
> check dual DSI mode like the code above. The purpose of dsi_manager module
> is to centralize dual DSI handler, so there has to be many checks.
>
> The current code should work with different cases,
> single-host-single-panel, dual-host-single-panel, dual-host-dual-panel and
> dual-host-independent-two-panels. If there is no panel for the host, we
> will report disconnected connector. If we want to convert to other
> interface type, i would prefer to have a fake dsi panel driver, to follow
> the current framework.
>

I think it will be a bit hard to incorporate fake panel support. I liked 
what's done in exynos/exynos_dp_core.c:

The driver figures out if the device node supports a panel connected via 
a bridge, or a DP connector. Based on this info, it registers either a 
bridge driver, or a usual DP connector.

I think it is fine to get this pulled as is. We can think later about 
whether the above or a fake panel approach would make more sense.

Thanks,
Archit

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