Re: [PATCH v10 5/5] drm/rockchip: Add dmc notifier in vop driver

[hl <hl@rock-chips.com>]

Hi Sean,

On 2016年09月07日 01:18, Sean Paul wrote:
> On Mon, Sep 5, 2016 at 1:06 AM, Lin Huang <hl@rock-chips.com> wrote:
>> when in ddr frequency scaling process, vop can not do enable or
>> disable operation, since in dcf we check vop clock to see whether
>> vop work. If vop work, dcf do ddr frequency scaling when vop
>> in vblank status, and we need to read vop register to check whether
>> vop go into vblank status. If vop not work, dcf can do ddr frequency
>> any time. So when do ddr frequency scaling, you disabled or enable
>> vop, there may two bad thing happen: 1, the panel flicker(when vop from
>> disable status change to enable). 2, kernel hang (when vop from enable
>> status change to disable, dcf need to read vblank status, but if you disable
>> vop clock, it can not get the status, it will lead soc dead) So we need
>> register to devfreq notifier, and we can get the dmc status. Also, when
>> there have two vop enabled, we need to disable dmc, since dcf only base
>> on one vop vblank time, so the other panel will flicker when do ddr
>> frequency scaling.
>>
>> Signed-off-by: Lin Huang <hl@rock-chips.com>
>> Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>
>> ---
>> Changes in v10:
>> - None
>>
>> Changes in v9:
>> - None
>>
>> Changes in v8:
>> - None
>>
>> Changes in v7:
>> - None
>>
>> Changes in v6:
>> - fix a build error
>>
>> Changes in v5:
>> - improve some nits
>>
>> Changes in v4:
>> - register notifier to devfreq_register_notifier
>> - use DEVFREQ_PRECHANGE and DEVFREQ_POSTCHANGE to get dmc status
>> - when two vop enable, disable dmc
>> - when two vop back to one vop, enable dmc
>>
>> Changes in v3:
>> - when do vop eanble/disable, dmc will wait until it finish
>>
>> Changes in v2:
>> - None
>>
>> Changes in v1:
>> - use wait_event instead usleep
>>
>>   drivers/gpu/drm/rockchip/rockchip_drm_vop.c | 116 ++++++++++++++++++++++++++++
>>   1 file changed, 116 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
>> index efbc41a..a73f3aa 100644
>> --- a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
>> +++ b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
>> @@ -19,6 +19,8 @@
>>   #include <drm/drm_crtc_helper.h>
>>   #include <drm/drm_plane_helper.h>
>>
>> +#include <linux/devfreq.h>
>> +#include <linux/devfreq-event.h>
>>   #include <linux/kernel.h>
>>   #include <linux/module.h>
>>   #include <linux/platform_device.h>
>> @@ -118,6 +120,13 @@ struct vop {
>>
>>          const struct vop_data *data;
>>
>> +       struct devfreq *devfreq;
>> +       struct devfreq_event_dev *devfreq_event_dev;
>> +       struct notifier_block dmc_nb;
>> +       int dmc_in_process;
>> +       int vop_switch_status;
>> +       wait_queue_head_t wait_dmc_queue;
>> +       wait_queue_head_t wait_vop_switch_queue;
>>          uint32_t *regsbak;
>>          void __iomem *regs;
>>
>> @@ -428,11 +437,47 @@ static void vop_dsp_hold_valid_irq_disable(struct vop *vop)
>>          spin_unlock_irqrestore(&vop->irq_lock, flags);
>>   }
>>
>> +static int dmc_notify(struct notifier_block *nb, unsigned long event,
>> +                     void *data)
>> +{
>> +       struct vop *vop = container_of(nb, struct vop, dmc_nb);
>> +
>> +       if (event == DEVFREQ_PRECHANGE) {
>> +               /*
>> +                * check if vop in enable or disable process,
>> +                * if yes, wait until it finishes, use 200ms as
>> +                * timeout.
>> +                */
>> +               if (!wait_event_timeout(vop->wait_vop_switch_queue,
>> +                                       !vop->vop_switch_status, HZ / 5))
>> +                       dev_warn(vop->dev,
>> +                                "Timeout waiting for vop swtich status\n");
>> +               vop->dmc_in_process = 1;
>> +       } else if (event == DEVFREQ_POSTCHANGE) {
>> +               vop->dmc_in_process = 0;
>> +               wake_up(&vop->wait_dmc_queue);
>> +       }
>> +
>> +       return NOTIFY_OK;
>> +}
>> +
>>   static int vop_enable(struct drm_crtc *crtc)
>>   {
>>          struct vop *vop = to_vop(crtc);
>> +       int num_enabled_crtc = 0;
>>          int ret;
>>
>> +       /*
>> +        * if in dmc scaling frequency process, wait until it finishes
>> +        * use 200ms as timeout time.
>> +        */
>> +       if (!wait_event_timeout(vop->wait_dmc_queue,
>> +                               !vop->dmc_in_process, HZ / 5))
>> +               dev_warn(vop->dev,
>> +                        "Timeout waiting for dmc when vop enable\n");
>> +
>
> This wait_event_timeout code is terribly racey (same goes above and below).
   No i use the vop_switch_status and dmc_in_progress to handle the vop 
and dmc racey,
    I assume this can fix the racey now. I do not better a idea now.
>
>
>> +       vop->vop_switch_status = 1;
>> +
>>          ret = pm_runtime_get_sync(vop->dev);
>>          if (ret < 0) {
>>                  dev_err(vop->dev, "failed to get pm runtime: %d\n", ret);
>> @@ -479,6 +524,21 @@ static int vop_enable(struct drm_crtc *crtc)
>>
>>          drm_crtc_vblank_on(crtc);
>>
>> +       vop->vop_switch_status = 0;
>> +       wake_up(&vop->wait_vop_switch_queue);
>> +
>> +       /* check how many VOPs in use now */
>> +       drm_for_each_crtc(crtc, vop->drm_dev) {
>> +               if (crtc->state->enable)
> I think you really want to check active, instead of enable.
Okay, i will check it, thanks.
>
>> +                       num_enabled_crtc++;
>> +       }
>> +
>> +       /* if enable two vop, need to disable dmc */
>> +       if ((num_enabled_crtc > 1) && vop->devfreq) {
>> +               if (vop->devfreq_event_dev)
>> +                       devfreq_event_disable_edev(vop->devfreq_event_dev);
>> +               devfreq_suspend_device(vop->devfreq);
>> +       }
> This really feels like something that should be handled somewhere
> else. I don't fully understand how this works, but it seems like this
> dependency should be handled where it actually matters, rather than
> building in a seemingly arbitrary restriction in the vop driver.
>
> Even if this is the best place for it, this needs to be refactored to
> eliminate the races that exist now.
>
> Sean
>
>>          return 0;
>>
>>   err_disable_aclk:
>> @@ -489,17 +549,31 @@ err_disable_hclk:
>>          clk_disable(vop->hclk);
>>   err_put_pm_runtime:
>>          pm_runtime_put_sync(vop->dev);
>> +       vop->vop_switch_status = 0;
>> +       wake_up(&vop->wait_vop_switch_queue);
>>          return ret;
>>   }
>>
>>   static void vop_crtc_disable(struct drm_crtc *crtc)
>>   {
>>          struct vop *vop = to_vop(crtc);
>> +       int num_enabled_crtc = 0;
>>          int i;
>>
>>          WARN_ON(vop->event);
>>
>>          /*
>> +        * if in dmc scaling frequency process, wait until it finish
>> +        * use 200ms as timeout time.
>> +        */
>> +       if (!wait_event_timeout(vop->wait_dmc_queue,
>> +                               !vop->dmc_in_process, HZ / 5))
>> +               dev_warn(vop->dev,
>> +                        "Timeout waiting for dmc when vop disable\n");
>> +
>> +       vop->vop_switch_status = 1;
>> +
>> +       /*
>>           * We need to make sure that all windows are disabled before we
>>           * disable that crtc. Otherwise we might try to scan from a destroyed
>>           * buffer later.
>> @@ -555,6 +629,24 @@ static void vop_crtc_disable(struct drm_crtc *crtc)
>>                  spin_unlock_irq(&crtc->dev->event_lock);
>>
>>                  crtc->state->event = NULL;
>> +
>> +       vop->vop_switch_status = 0;
>> +       wake_up(&vop->wait_vop_switch_queue);
>> +
>> +       /* check how many VOPs in use now */
>> +       drm_for_each_crtc(crtc, vop->drm_dev) {
>> +               if (crtc->state->enable)
>> +                       num_enabled_crtc++;
>> +       }
>> +
>> +       /*
>> +        * if num_enabled_crtc = 1 now, it means 2 vop enabled
>> +        * change to 1 vop enabled  need to enable dmc again.
>> +        */
>> +       if ((num_enabled_crtc == 1) && vop->devfreq) {
>> +               if (vop->devfreq_event_dev)
>> +                       devfreq_event_enable_edev(vop->devfreq_event_dev);
>> +               devfreq_resume_device(vop->devfreq);
>>          }
>>   }
>>
>> @@ -1413,6 +1505,8 @@ static int vop_bind(struct device *dev, struct device *master, void *data)
>>          struct drm_device *drm_dev = data;
>>          struct vop *vop;
>>          struct resource *res;
>> +       struct devfreq *devfreq;
>> +       struct devfreq_event_dev *event_dev;
>>          size_t alloc_size;
>>          int ret, irq;
>>
>> @@ -1474,6 +1568,28 @@ static int vop_bind(struct device *dev, struct device *master, void *data)
>>                  return ret;
>>
>>          pm_runtime_enable(&pdev->dev);
>> +
>> +       init_waitqueue_head(&vop->wait_vop_switch_queue);
>> +       vop->vop_switch_status = 0;
>> +       init_waitqueue_head(&vop->wait_dmc_queue);
>> +       vop->dmc_in_process = 0;
>> +
>> +       devfreq = devfreq_get_devfreq_by_phandle(dev, 0);
>> +       if (IS_ERR(devfreq))
>> +               goto out;
>> +
>> +       vop->devfreq = devfreq;
>> +       vop->dmc_nb.notifier_call = dmc_notify;
>> +       devfreq_register_notifier(vop->devfreq, &vop->dmc_nb,
>> +                                 DEVFREQ_TRANSITION_NOTIFIER);
>> +
>> +       event_dev = devfreq_event_get_edev_by_phandle(vop->devfreq->dev.parent,
>> +                                                     0);
>> +       if (IS_ERR(event_dev))
>> +               goto out;
>> +
>> +       vop->devfreq_event_dev = event_dev;
>> +out:
>>          return 0;
>>   }
>>
>> --
>> 2.6.6
>>
>
>

-- 
Lin Huang