Re: [PATCH v8 17/18] media: ti: j721e-csi2rx: Support runtime suspend

[Jai Luthra <jai.luthra@ideasonboard.com>]

Hi Sakari,

Thanks for the review.

Quoting Sakari Ailus (2025-11-20 18:46:14)
> Hi Rishikesh,
> 
> On Wed, Nov 12, 2025 at 05:24:58PM +0530, Rishikesh Donadkar wrote:
> > From: Jai Luthra <jai.luthra@ideasonboard.com>
> > 
> > Add support for runtime power-management to enable powering off the
> > shared power domain between Cadence CSI2RX and TI CSI2RX wrapper when
> > the device(s) are not in use.
> > 
> > When powering off the IP, the PSI-L endpoint loses the paired DMA
> > channels. Thus we have to release the DMA channels at runtime suspend
> > and request them again at resume.
> > 
> > Tested-by: Rishikesh Donadkar <r-donadkar@ti.com>
> > Reviewed-by: Rishikesh Donadkar <r-donadkar@ti.com>
> > Signed-off-by: Jai Luthra <jai.luthra@ideasonboard.com>
> > Signed-off-by: Rishikesh Donadkar <r-donadkar@ti.com>
> > ---
> >  drivers/media/platform/ti/Kconfig             |  1 +
> >  .../platform/ti/j721e-csi2rx/j721e-csi2rx.c   | 55 ++++++++++++++++++-
> >  2 files changed, 54 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/media/platform/ti/Kconfig b/drivers/media/platform/ti/Kconfig
> > index 3bc4aa35887e6..a808063e24779 100644
> > --- a/drivers/media/platform/ti/Kconfig
> > +++ b/drivers/media/platform/ti/Kconfig
> > @@ -70,6 +70,7 @@ config VIDEO_TI_J721E_CSI2RX
> >       depends on VIDEO_CADENCE_CSI2RX
> >       depends on PHY_CADENCE_DPHY_RX || COMPILE_TEST
> >       depends on ARCH_K3 || COMPILE_TEST
> > +     depends on PM
> >       select VIDEOBUF2_DMA_CONTIG
> >       select V4L2_FWNODE
> >       help
> > diff --git a/drivers/media/platform/ti/j721e-csi2rx/j721e-csi2rx.c b/drivers/media/platform/ti/j721e-csi2rx/j721e-csi2rx.c
> > index 528041ee78cf3..21e032c64b901 100644
> > --- a/drivers/media/platform/ti/j721e-csi2rx/j721e-csi2rx.c
> > +++ b/drivers/media/platform/ti/j721e-csi2rx/j721e-csi2rx.c
> > @@ -13,6 +13,7 @@
> >  #include <linux/module.h>
> >  #include <linux/of_platform.h>
> >  #include <linux/platform_device.h>
> > +#include <linux/pm_runtime.h>
> >  #include <linux/property.h>
> >  
> >  #include <media/cadence/cdns-csi2rx.h>
> > @@ -963,12 +964,16 @@ static int ti_csi2rx_start_streaming(struct vb2_queue *vq, unsigned int count)
> >       unsigned long flags;
> >       int ret = 0;
> >  
> > +     ret = pm_runtime_resume_and_get(csi->dev);
> > +     if (ret)
> > +             return ret;
> > +
> >       spin_lock_irqsave(&dma->lock, flags);
> >       if (list_empty(&dma->queue))
> >               ret = -EIO;
> >       spin_unlock_irqrestore(&dma->lock, flags);
> >       if (ret)
> > -             return ret;
> > +             goto err;
> >  
> >       ret = video_device_pipeline_start(&ctx->vdev, &csi->pipe);
> >       if (ret)
> > @@ -1024,6 +1029,8 @@ static int ti_csi2rx_start_streaming(struct vb2_queue *vq, unsigned int count)
> >       writel(0, csi->shim + SHIM_DMACNTX(ctx->idx));
> >  err:
> >       ti_csi2rx_cleanup_buffers(ctx, VB2_BUF_STATE_QUEUED);
> > +     pm_runtime_put(csi->dev);
> > +
> >       return ret;
> >  }
> >  
> > @@ -1055,6 +1062,7 @@ static void ti_csi2rx_stop_streaming(struct vb2_queue *vq)
> >  
> >       ti_csi2rx_stop_dma(ctx);
> >       ti_csi2rx_cleanup_buffers(ctx, VB2_BUF_STATE_ERROR);
> > +     pm_runtime_put(csi->dev);
> >  }
> >  
> >  static const struct vb2_ops csi_vb2_qops = {
> > @@ -1261,7 +1269,9 @@ static void ti_csi2rx_cleanup_notifier(struct ti_csi2rx_dev *csi)
> >  
> >  static void ti_csi2rx_cleanup_ctx(struct ti_csi2rx_ctx *ctx)
> >  {
> > -     dma_release_channel(ctx->dma.chan);
> > +     if (!pm_runtime_status_suspended(ctx->csi->dev))
> 
> What's the motivation for this change? Do the DMA channel need to be
> released only if the device's RPM status isn't suspended?
> 
> Is there a guarantee Runtime PM is disabled when the function is called?
> Otherwise there's no guarantee state change couldn't occur.
> 

The channels are released during PM runtime suspend, and re-paired in
resume. I like Tomi's suggestion of removing the channel logic from
init/cleanup_ctx altogether, which will also get rid of this change.

> > +             dma_release_channel(ctx->dma.chan);
> > +
> >       vb2_queue_release(&ctx->vidq);
> >  
> >       video_unregister_device(&ctx->vdev);
> > @@ -1512,6 +1522,39 @@ static int ti_csi2rx_init_ctx(struct ti_csi2rx_ctx *ctx)
> >       return ret;
> >  }
> >  
> > +static int ti_csi2rx_runtime_suspend(struct device *dev)
> > +{
> > +     struct ti_csi2rx_dev *csi = dev_get_drvdata(dev);
> > +     int i;
> > +
> > +     if (csi->enable_count != 0)
> > +             return -EBUSY;
> > +
> > +     for (i = 0; i < csi->num_ctx; i++)
> > +             dma_release_channel(csi->ctx[i].dma.chan);
> > +
> > +     return 0;
> > +}
> > +
> > +static int ti_csi2rx_runtime_resume(struct device *dev)
> > +{
> > +     struct ti_csi2rx_dev *csi = dev_get_drvdata(dev);
> > +     int ret, i;
> > +
> > +     for (i = 0; i < csi->num_ctx; i++) {
> 
> You could declare i (as unsigned int) here.
> 
> The same for ret actually.
> 

Will do.

> > +             ret = ti_csi2rx_init_dma(&csi->ctx[i]);
> > +             if (ret)
> > +                     return ret;
> > +     }
> > +
> > +     return 0;
> > +}
> > +
> > +static const struct dev_pm_ops ti_csi2rx_pm_ops = {
> > +     RUNTIME_PM_OPS(ti_csi2rx_runtime_suspend, ti_csi2rx_runtime_resume,
> > +                    NULL)
> > +};
> > +
> >  static int ti_csi2rx_probe(struct platform_device *pdev)
> >  {
> >       struct device_node *np = pdev->dev.of_node;
> > @@ -1579,6 +1622,10 @@ static int ti_csi2rx_probe(struct platform_device *pdev)
> >               goto err_notifier;
> >       }
> >  
> > +     pm_runtime_set_active(csi->dev);
> > +     pm_runtime_enable(csi->dev);
> 
> Note that the sub-device driver's UAPI may be already available to users
> when the async sub-device is registered. Therefore you'll need enable
> runtime PM before that.
> 

The only place where the driver actually writes registers to the hardware
is in .start_streaming(), which I presume can only be called after the
whole media pipeline is probed?

> > +     pm_request_idle(csi->dev);
> > +
> >       return 0;
> >  
> >  err_notifier:
> > @@ -1609,6 +1656,9 @@ static void ti_csi2rx_remove(struct platform_device *pdev)
> >       mutex_destroy(&csi->mutex);
> >       dma_free_coherent(csi->dev, csi->drain.len, csi->drain.vaddr,
> >                         csi->drain.paddr);
> 
> Is there a guarantee the device is in a particular runtime PM state here,
> e.g. suspended?
> 

I don't think so, userspace could attempt to remove the device while
streaming. Good point, I haven't checked what all goes wrong in that case.

> > +     pm_runtime_disable(&pdev->dev);
> > +     pm_runtime_set_suspended(&pdev->dev);
> > +
> >  }
> >  
> >  static const struct of_device_id ti_csi2rx_of_match[] = {
> > @@ -1623,6 +1673,7 @@ static struct platform_driver ti_csi2rx_pdrv = {
> >       .driver = {
> >               .name = TI_CSI2RX_MODULE_NAME,
> >               .of_match_table = ti_csi2rx_of_match,
> > +             .pm             = &ti_csi2rx_pm_ops,
> >       },
> >  };
> >  
> 
> -- 
> Kind regards,
> 
> Sakari Ailus

Thanks,
Jai