Re: [PATCH 1/2] drm/dp_aux: Use non-cyclic idr, add suffix option for aux device

["Li, Sun peng (Leo)" <Sunpeng.Li-5C7GfCeVMHo@public.gmane.org>]

On 2019-04-16 6:16 p.m., Lyude Paul wrote:
> Sorry for the slow response, I've been really busy ;_;

No worries :)

> 
> On Fri, 2019-04-12 at 12:05 -0400, sunpeng.li@amd.com wrote:
>> From: Leo Li <sunpeng.li@amd.com>
>>
>> In preparation for adding aux devices for DP MST:
>>
>> 1. A non-cyclic idr is used for the device minor version. That way,
>>     hotplug cycling MST devices won't needlessly increment the minor
>>     version index.
> 
> I really like this btw, cyclic idrs are really annoying for drm_dp_aux_dev,
> even outside of MST (try reloading a drm driver a couple of times and you'll
> understand ;). I think we should split this into another commit though
> 
>> 2. A suffix option is added to the aux device file name. It can be used
>>     to identify the corresponding MST device.
> 
> I like this idea, but I think there may be a better way that we can do this.
> Using /dev/nvme* as an example, we have the standard dev paths (/dev/nvme0,
> /dev/nvme0n1, etc.). But we can also access them through /dev/disk/by-
> {id,label,partlabel,partuuid,path,uuid}.
> 
> So what if we added something similar for aux devices? We start off with the
> standard /dev/drm_dp_aux*, then provide more descriptive symlinks and
> directories:
> 
> (feel free to come up with better naming then this if you can)
> 
> /dev/drm_dp_aux/card0-DP-1 -> /dev/drm_dp_aux1
> /dev/drm_dp_aux/card0-DP-2 -> /dev/drm_dp_aux2
> etc.

That does sound neater - although FWICT, this will have to be done with
udev rules?

I took a brief look at how that's done for storage devices. It looks
like they have rules defined in
/lib/udev/rules.d/60-persistent-storage.rules that manages the "by-x"
symlinks.

To make this happen for aux devices, what we could do is attach sysfs
attributes to the device. It can then be parsed by udev in a similar
fashion. Currently, only 'name' attribute is attached, as seen in
drm_dp_aux_dev.c (after name_show()).

Thanks,
Leo

> 
>>
>> Signed-off-by: Leo Li <sunpeng.li@amd.com>
>> ---
>>   drivers/gpu/drm/drm_crtc_helper_internal.h | 5 +++--
>>   drivers/gpu/drm/drm_dp_aux_dev.c           | 8 ++++----
>>   drivers/gpu/drm/drm_dp_helper.c            | 2 +-
>>   3 files changed, 8 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_crtc_helper_internal.h
>> b/drivers/gpu/drm/drm_crtc_helper_internal.h
>> index b5ac158..9f0907b 100644
>> --- a/drivers/gpu/drm/drm_crtc_helper_internal.h
>> +++ b/drivers/gpu/drm/drm_crtc_helper_internal.h
>> @@ -46,7 +46,7 @@ static inline int drm_fb_helper_modinit(void)
>>   #ifdef CONFIG_DRM_DP_AUX_CHARDEV
>>   int drm_dp_aux_dev_init(void);
>>   void drm_dp_aux_dev_exit(void);
>> -int drm_dp_aux_register_devnode(struct drm_dp_aux *aux);
>> +int drm_dp_aux_register_devnode(struct drm_dp_aux *aux, const char
>> *suffix);
>>   void drm_dp_aux_unregister_devnode(struct drm_dp_aux *aux);
>>   #else
>>   static inline int drm_dp_aux_dev_init(void)
>> @@ -58,7 +58,8 @@ static inline void drm_dp_aux_dev_exit(void)
>>   {
>>   }
>>   
>> -static inline int drm_dp_aux_register_devnode(struct drm_dp_aux *aux)
>> +static inline int drm_dp_aux_register_devnode(struct drm_dp_aux *aux,
>> +					      const char *suffix)
>>   {
>>   	return 0;
>>   }
>> diff --git a/drivers/gpu/drm/drm_dp_aux_dev.c
>> b/drivers/gpu/drm/drm_dp_aux_dev.c
>> index 0e4f25d..2310a67 100644
>> --- a/drivers/gpu/drm/drm_dp_aux_dev.c
>> +++ b/drivers/gpu/drm/drm_dp_aux_dev.c
>> @@ -80,8 +80,7 @@ static struct drm_dp_aux_dev *alloc_drm_dp_aux_dev(struct
>> drm_dp_aux *aux)
>>   	kref_init(&aux_dev->refcount);
>>   
>>   	mutex_lock(&aux_idr_mutex);
>> -	index = idr_alloc_cyclic(&aux_idr, aux_dev, 0, DRM_AUX_MINORS,
>> -				 GFP_KERNEL);
>> +	index = idr_alloc(&aux_idr, aux_dev, 0, DRM_AUX_MINORS, GFP_KERNEL);
>>   	mutex_unlock(&aux_idr_mutex);
>>   	if (index < 0) {
>>   		kfree(aux_dev);
>> @@ -290,7 +289,7 @@ void drm_dp_aux_unregister_devnode(struct drm_dp_aux
>> *aux)
>>   	kref_put(&aux_dev->refcount, release_drm_dp_aux_dev);
>>   }
>>   
>> -int drm_dp_aux_register_devnode(struct drm_dp_aux *aux)
>> +int drm_dp_aux_register_devnode(struct drm_dp_aux *aux, const char *suffix)
>>   {
>>   	struct drm_dp_aux_dev *aux_dev;
>>   	int res;
>> @@ -301,7 +300,8 @@ int drm_dp_aux_register_devnode(struct drm_dp_aux *aux)
>>   
>>   	aux_dev->dev = device_create(drm_dp_aux_dev_class, aux->dev,
>>   				     MKDEV(drm_dev_major, aux_dev->index),
>> NULL,
>> -				     "drm_dp_aux%d", aux_dev->index);
>> +				     "drm_dp_aux%d%s", aux_dev->index,
>> +				     suffix ? suffix : "");
>>   	if (IS_ERR(aux_dev->dev)) {
>>   		res = PTR_ERR(aux_dev->dev);
>>   		aux_dev->dev = NULL;
>> diff --git a/drivers/gpu/drm/drm_dp_helper.c
>> b/drivers/gpu/drm/drm_dp_helper.c
>> index e2266ac..13f1005 100644
>> --- a/drivers/gpu/drm/drm_dp_helper.c
>> +++ b/drivers/gpu/drm/drm_dp_helper.c
>> @@ -1143,7 +1143,7 @@ int drm_dp_aux_register(struct drm_dp_aux *aux)
>>   	strlcpy(aux->ddc.name, aux->name ? aux->name : dev_name(aux->dev),
>>   		sizeof(aux->ddc.name));
>>   
>> -	ret = drm_dp_aux_register_devnode(aux);
>> +	ret = drm_dp_aux_register_devnode(aux, NULL);
>>   	if (ret)
>>   		return ret;
>>   
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