Re: [PATCH v2 4/5] drm/exynos: Initialize ptn3460 if present

[Sean Paul]

On Fri, Oct 4, 2013 at 11:01 AM, Inki Dae <inki.dae@xxxxxxxxxxx> wrote:
>
>
>> -----Original Message-----
>> From: Sean Paul [mailto:seanpaul@xxxxxxxxxxxx]
>> Sent: Friday, October 04, 2013 11:17 PM
>> To: Inki Dae
>> Cc: Kukjin Kim; DRI mailing list; linux-samsung-soc@xxxxxxxxxxxxxxx;
>> linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; linux-
>> doc@xxxxxxxxxxxxxxx; devicetree@xxxxxxxxxxxxxxx; Dave Airlie
>> Subject: Re: [PATCH v2 4/5] drm/exynos: Initialize ptn3460 if present
>>
>> On Fri, Oct 4, 2013 at 12:18 AM, Inki Dae <inki.dae@xxxxxxxxxxx> wrote:
>> > 2013/10/4 Sean Paul <seanpaul@xxxxxxxxxxxx>:
>> >> On Thu, Oct 3, 2013 at 10:29 PM, Inki Dae <inki.dae@xxxxxxxxxxx> wrote:
>> >>> 2013/10/4 Sean Paul <seanpaul@xxxxxxxxxxxx>:
>> >>>> This patch adds code to look for the ptn3460 in the device tree file
>> on
>> >>>> exynos initialization. If ptn node is found, the driver will
>> initialize
>> >>>> the ptn3460 driver and skip creating a DP connector (since the bridge
>> >>>> driver will register its own connector).
>> >>>>
>> >>>> Signed-off-by: Sean Paul <seanpaul@xxxxxxxxxxxx>
>> >>>> ---
>> >>>>
>> >>>> v2:
>> >>>>         - Changed include from of_i2c.h to i2c.h
>> >>>>         - Changed of_find_by_name to of_find_compatible
>> >>>>
>> >>>>  drivers/gpu/drm/exynos/exynos_drm_core.c | 44
>> +++++++++++++++++++++++++++++++-
>> >>>>  1 file changed, 43 insertions(+), 1 deletion(-)
>> >>>>
>> >>>> diff --git a/drivers/gpu/drm/exynos/exynos_drm_core.c
>> b/drivers/gpu/drm/exynos/exynos_drm_core.c
>> >>>> index 1bef6dc..08ca4f9 100644
>> >>>> --- a/drivers/gpu/drm/exynos/exynos_drm_core.c
>> >>>> +++ b/drivers/gpu/drm/exynos/exynos_drm_core.c
>> >>>> @@ -12,7 +12,9 @@
>> >>>>   * option) any later version.
>> >>>>   */
>> >>>>
>> >>>> +#include <linux/i2c.h>
>> >>>>  #include <drm/drmP.h>
>> >>>> +#include <drm/bridge/ptn3460.h>
>> >>>>  #include "exynos_drm_drv.h"
>> >>>>  #include "exynos_drm_encoder.h"
>> >>>>  #include "exynos_drm_connector.h"
>> >>>> @@ -20,6 +22,40 @@
>> >>>>
>> >>>>  static LIST_HEAD(exynos_drm_subdrv_list);
>> >>>>
>> >>>> +struct bridge_init {
>> >>>> +       struct i2c_client *client;
>> >>>> +       struct device_node *node;
>> >>>> +};
>> >>>> +
>> >>>> +static bool find_bridge(const char *compat, struct bridge_init
>> *bridge)
>> >>>> +{
>> >>>> +       bridge->client = NULL;
>> >>>> +       bridge->node = of_find_compatible_node(NULL, NULL, compat);
>> >>>
>> >>> Then, shouldn't the lvds-bridge driver be implemented as i2c driver so
>> >>> that such tricky isn't needed? Is there any reason you use such tricky
>> >>> codes?
>> >>>
>> >>
>> >> This is what I was explaining earlier today. If the bridge driver is
>> >> just an i2c driver, it won't get a pointer to drm_device, and can't
>> >> register itself as a drm_bridge or drm_connector. To solve this, you
>> >> need the ptn3460_init callback.
>> >>
>> >
>> > No, I think you can use sub driver. how about registering to exynos
>> > drm core that driver using exynos_drm_subdrv_register function after
>> > probed? Is there something I am missing?
>> >
>>
>> The ptn driver isn't exynos-specific, so I don't think making it an
>> exynos_drm_subdrv is appropriate.
>>
>
> I _really know_ that the ptn driver isn't exynos-specific. I mean that you
> can use exynos_drm_subdrv somehow. ie. you can add a new bridge module
> specific to exynos, and this module can register its own sub driver at end
> of probe. Why do you try to use such tricky codes?
>

So I create a new exynos_lvds_driver which is an i2c driver. When that
probes, all it does is register that driver as an exynos_drm_subdrv.
Then in the subdrv probe I call into ptn3460_init?

That seems a lot more tricky than just calling ptn3460_init directly...

Sean


> Thanks,
> Inki Dae
>
>> Sean
>>
>> >
>> >> If it's an i2c driver with the ptn3460_init callback, where it parses
>> >> the dt in probe, then you have a race between the ptn probe and the
>> >> ptn init/drm hooks. ie: it's possible drm will initialize and call
>> >> disable/post_disable/pre_enable/enable before things have been probed.
>> >
>> > And also, exynos drm core will call a probe callback of the sub driver
>> > after _drm is initialized_. Is there something I am missing?
>> >
>> >> To solve this, you need to use some global state and/or locking.
>> >>
>> >> So, to summarize. We can have this of_find_compatible with a init
>> >> callback, or we can have an i2c driver + global state/locking + init
>> >> callback. I chose the former, since it seemed easier.
>> >>
>> >> If you have a better way to achieve this, I'm definitely interested,
>> >> but I saw this as the lesser of two evils.
>> >>
>> >> Sean
>> >>
>> >>> I think you need to implement the lvds-bridge driver as i2c driver,
>> >>> and then consider how to take care of this. I mean let's find a better
>> >>> way how we could take care of the i2c based driver in exynos drm
>> >>> framework or driver. In all cases, such tricky codes are not good.
>> >>>
>> >>>> +       if (!bridge->node)
>> >>>> +               return false;
>> >>>> +
>> >>>> +       bridge->client = of_find_i2c_device_by_node(bridge->node);
>> >>>> +       if (!bridge->client)
>> >>>> +               return false;
>> >>>> +
>> >>>> +       return true;
>> >>>> +}
>> >>>> +
>> >>>> +/* returns the number of bridges attached */
>> >>>> +static int exynos_drm_attach_lcd_bridge(struct drm_device *dev,
>> >>>> +               struct drm_encoder *encoder)
>> >>>> +{
>> >>>> +       struct bridge_init bridge;
>> >>>> +       int ret;
>> >>>> +
>> >>>> +       if (find_bridge("nxp,ptn3460", &bridge)) {
>> >>>> +               ret = ptn3460_init(dev, encoder, bridge.client,
>> bridge.node);
>> >>>> +               if (!ret)
>> >>>> +                       return 1;
>> >>>> +       }
>> >>>> +       return 0;
>> >>>> +}
>> >>>> +
>> >>>>  static int exynos_drm_create_enc_conn(struct drm_device *dev,
>> >>>>                                         struct exynos_drm_subdrv
> *subdrv)
>> >>>>  {
>> >>>> @@ -36,6 +72,13 @@ static int exynos_drm_create_enc_conn(struct
>> drm_device *dev,
>> >>>>                 DRM_ERROR("failed to create encoder\n");
>> >>>>                 return -EFAULT;
>> >>>>         }
>> >>>> +       subdrv->encoder = encoder;
>> >>>> +
>> >>>> +       if (subdrv->manager->display_ops->type ==
>> EXYNOS_DISPLAY_TYPE_LCD) {
>> >>>> +               ret = exynos_drm_attach_lcd_bridge(dev, encoder);
>> >>>> +               if (ret)
>> >>>> +                       return 0;
>> >>>> +       }
>> >>>>
>> >>>>         /*
>> >>>>          * create and initialize a connector for this sub driver and
>> >>>> @@ -48,7 +91,6 @@ static int exynos_drm_create_enc_conn(struct
>> drm_device *dev,
>> >>>>                 goto err_destroy_encoder;
>> >>>>         }
>> >>>>
>> >>>> -       subdrv->encoder = encoder;
>> >>>>         subdrv->connector = connector;
>> >>>>
>> >>>>         return 0;
>> >>>> --
>> >>>> 1.8.4
>> >>>>
>> >>>> --
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