Re: [PATCH v5 6/6] drm/bridge/sii8620: use micro-USB cable detection logic to detect MHL

[Andrzej Hajda <a.hajda@samsung.com>]

On 27.02.2018 23:26, Chanwoo Choi wrote:
> Hi,
>
> On 2018년 02월 27일 21:05, Andrzej Hajda wrote:
>> On 27.02.2018 12:08, Chanwoo Choi wrote:
>>> Hi,
>>>
>>> On 2018년 02월 27일 16:11, Andrzej Hajda wrote:
>>>> From: Maciej Purski <m.purski@samsung.com>
>>>>
>>>> Currently MHL chip must be turned on permanently to detect MHL cable. It
>>>> duplicates micro-USB controller's (MUIC) functionality and consumes
>>>> unnecessary power. Lets use extcon attached to MUIC to enable MHL chip
>>>> only if it detects MHL cable.
>>>>
>>>> Signed-off-by: Maciej Purski <m.purski@samsung.com>
>>>> Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
>>>> ---
>>>> v5: updated extcon API
>>>>
>>>> This is rework of the patch by Maciej with following changes:
>>>> - use micro-USB port bindings to get extcon, instead of extcon property,
>>>> - fixed remove sequence,
>>>> - fixed extcon get state logic.
>>>>
>>>> Code finding extcon node is hacky IMO, I guess ultimately it should be done
>>>> via some framework (maybe even extcon), or at least via helper, I hope it
>>>> can stay as is until the proper solution will be merged.
>>>>
>>>> Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
>>>> ---
>>>>  drivers/gpu/drm/bridge/sil-sii8620.c | 97 ++++++++++++++++++++++++++++++++++--
>>>>  1 file changed, 94 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/bridge/sil-sii8620.c b/drivers/gpu/drm/bridge/sil-sii8620.c
>>>> index 9e785b8e0ea2..62b0adabcac2 100644
>>>> --- a/drivers/gpu/drm/bridge/sil-sii8620.c
>>>> +++ b/drivers/gpu/drm/bridge/sil-sii8620.c
>>>> @@ -17,6 +17,7 @@
>>>>  
>>>>  #include <linux/clk.h>
>>>>  #include <linux/delay.h>
>>>> +#include <linux/extcon.h>
>>>>  #include <linux/gpio/consumer.h>
>>>>  #include <linux/i2c.h>
>>>>  #include <linux/interrupt.h>
>>>> @@ -25,6 +26,7 @@
>>>>  #include <linux/list.h>
>>>>  #include <linux/module.h>
>>>>  #include <linux/mutex.h>
>>>> +#include <linux/of_graph.h>
>>>>  #include <linux/regulator/consumer.h>
>>>>  #include <linux/slab.h>
>>>>  
>>>> @@ -81,6 +83,10 @@ struct sii8620 {
>>>>  	struct edid *edid;
>>>>  	unsigned int gen2_write_burst:1;
>>>>  	enum sii8620_mt_state mt_state;
>>>> +	struct extcon_dev *extcon;
>>>> +	struct notifier_block extcon_nb;
>>>> +	struct work_struct extcon_wq;
>>>> +	int cable_state;
>>>>  	struct list_head mt_queue;
>>>>  	struct {
>>>>  		int r_size;
>>>> @@ -2175,6 +2181,77 @@ static void sii8620_init_rcp_input_dev(struct sii8620 *ctx)
>>>>  	ctx->rc_dev = rc_dev;
>>>>  }
>>>>  
>>>> +static void sii8620_cable_out(struct sii8620 *ctx)
>>>> +{
>>>> +	disable_irq(to_i2c_client(ctx->dev)->irq);
>>>> +	sii8620_hw_off(ctx);
>>>> +}
>>>> +
>>>> +static void sii8620_extcon_work(struct work_struct *work)
>>>> +{
>>>> +	struct sii8620 *ctx =
>>>> +		container_of(work, struct sii8620, extcon_wq);
>>>> +	int state = extcon_get_state(ctx->extcon, EXTCON_DISP_MHL);
>>>> +
>>>> +	if (state == ctx->cable_state)
>>>> +		return;
>>>> +
>>>> +	ctx->cable_state = state;
>>>> +
>>>> +	if (state > 0)
>>>> +		sii8620_cable_in(ctx);
>>>> +	else
>>>> +		sii8620_cable_out(ctx);
>>>> +}
>>>> +
>>>> +static int sii8620_extcon_notifier(struct notifier_block *self,
>>>> +			unsigned long event, void *ptr)
>>>> +{
>>>> +	struct sii8620 *ctx =
>>>> +		container_of(self, struct sii8620, extcon_nb);
>>>> +
>>>> +	schedule_work(&ctx->extcon_wq);
>>>> +
>>>> +	return NOTIFY_DONE;
>>>> +}
>>>> +
>>>> +static int sii8620_extcon_init(struct sii8620 *ctx)
>>>> +{
>>>> +	struct extcon_dev *edev;
>>>> +	struct device_node *musb, *muic;
>>>> +	int ret;
>>>> +
>>>> +	/* get micro-USB connector node */
>>>> +	musb = of_graph_get_remote_node(ctx->dev->of_node, 1, -1);
>>>> +	/* next get micro-USB Interface Controller node */
>>>> +	muic = of_get_next_parent(musb);
>>>> +
>>>> +	if (!muic) {
>>>> +		dev_info(ctx->dev, "no extcon found, switching to 'always on' mode\n");
>>>> +		return 0;
>>>> +	}
>>>> +
>>>> +	edev = extcon_find_edev_by_node(muic);
>>>> +	of_node_put(muic);
>>>> +	if (IS_ERR(edev)) {
>>>> +		if (PTR_ERR(edev) == -EPROBE_DEFER)
>>>> +			return -EPROBE_DEFER;
>>>> +		dev_err(ctx->dev, "Invalid or missing extcon\n");
>>>> +		return PTR_ERR(edev);
>>>> +	}
>>>> +
>>>> +	ctx->extcon = edev;
>>>> +	ctx->extcon_nb.notifier_call = sii8620_extcon_notifier;
>>>> +	INIT_WORK(&ctx->extcon_wq, sii8620_extcon_work);
>>>> +	ret = extcon_register_notifier(edev, EXTCON_DISP_MHL, &ctx->extcon_nb);
>>> You better to use devm_extcon_register_notifier().
>> With devm version I risk that in case of device unbind notification will
>> be called after .remove callback, it seems to me quite dangerous. Or am
>> I missing something?
> If you use the cancel_work_sync() in remove() instead of flush_work(),
> you can use the 'devm_extcon_*'.

cancel_work_sync() does not prevent works scheduled later from execution
[1] and this scenario is possible with devm_extcon_register_notifier()
and cancel_work_sync().
So we end up with:
    sii8620_remove() calls cancel_work_sync()
...
    notifier(called asynchronously) schedules sii8620_extcon_work()
...
    notifier is removed by devm framework
    sii8620 context is destroyed by devm framework
...
    sii8620_extcon_work is executed on destroyed context !!! BUG !!!

For me it seems that devm_extcon_register_notifier is not safe in this case.

[1]: Since documentation was not clear I have performed live test
confirming my suspicions.

Regards
Andrzej

>
>> Regards
>> Andrzej
>>
>>>> +	if (ret) {
>>>> +		dev_err(ctx->dev, "failed to register notifier for MHL\n");
>>>> +		return ret;
>>>> +	}
>>>> +
>>>> +	return 0;
>>>> +}
>>>> +
>>>>  static inline struct sii8620 *bridge_to_sii8620(struct drm_bridge *bridge)
>>>>  {
>>>>  	return container_of(bridge, struct sii8620, bridge);
>>>> @@ -2307,13 +2384,20 @@ static int sii8620_probe(struct i2c_client *client,
>>>>  	if (ret)
>>>>  		return ret;
>>>>  
>>>> +	ret = sii8620_extcon_init(ctx);
>>>> +	if (ret < 0) {
>>>> +		dev_err(ctx->dev, "failed to initialize EXTCON\n");
>>>> +		return ret;
>>>> +	}
>>>> +
>>>>  	i2c_set_clientdata(client, ctx);
>>>>  
>>>>  	ctx->bridge.funcs = &sii8620_bridge_funcs;
>>>>  	ctx->bridge.of_node = dev->of_node;
>>>>  	drm_bridge_add(&ctx->bridge);
>>>>  
>>>> -	sii8620_cable_in(ctx);
>>>> +	if (!ctx->extcon)
>>>> +		sii8620_cable_in(ctx);
>>>>  
>>>>  	return 0;
>>>>  }
>>>> @@ -2322,8 +2406,15 @@ static int sii8620_remove(struct i2c_client *client)
>>>>  {
>>>>  	struct sii8620 *ctx = i2c_get_clientdata(client);
>>>>  
>>>> -	disable_irq(to_i2c_client(ctx->dev)->irq);
>>>> -	sii8620_hw_off(ctx);
>>>> +	if (ctx->extcon) {
>>>> +		extcon_unregister_notifier(ctx->extcon, EXTCON_DISP_MHL,
>>>> +					   &ctx->extcon_nb);
>>> Don't need to unregister the notifier if using devm_extcon_register_notifier().
>>>
>>>> +		flush_work(&ctx->extcon_wq);
>>>> +		if (ctx->cable_state > 0)
>>>> +			sii8620_cable_out(ctx);
>>>> +	} else {
>>>> +		sii8620_cable_out(ctx);
>>>> +	}
>>>>  	drm_bridge_remove(&ctx->bridge);
>>>>  
>>>>  	return 0;
>>>>
>>> If you use the resource managed function (devm_extcon_register_notifier), Looks good to me.
>>> Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>
>>>
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