linux-kernel - Re: [PATCH] dmaengine: dw-edma: Remove runtime PM support

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Date:   Fri, 19 Aug 2022 14:10:18 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     gustavo.pimentel@...opsys.com, vkoul@...nel.org
Cc:     dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org,
        Serge Semin <fancer.lancer@...il.com>,
        Frank Li <Frank.Li@....com>
Subject: Re: [PATCH] dmaengine: dw-edma: Remove runtime PM support

On Thu, May 12, 2022 at 02:06:12PM +0530, Manivannan Sadhasivam wrote:
> Currently, the dw-edma driver enables the runtime_pm for parent device
> (chip->dev) and increments/decrements the refcount during alloc/free
> chan resources callbacks.
> 
> This leads to a problem when the eDMA driver has been probed, but the
> channels were not used. This scenario can happen when the DW PCIe driver
> probes eDMA driver successfully, but the PCI EPF driver decides not to
> use eDMA channels and use iATU instead for PCI transfers.
> 
> In this case, the underlying device would be runtime suspended due to
> pm_runtime_enable() in dw_edma_probe() and the PCI EPF driver would have
> no knowledge of it.
> 
> Ideally, the eDMA driver should not be the one doing the runtime PM of
> the parent device. The responsibility should instead belong to the client
> drivers like PCI EPF.
> 
> So let's remove the runtime PM support from eDMA driver.
> 
> Cc: Serge Semin <fancer.lancer@...il.com>
> Cc: Frank Li <Frank.Li@....com>
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>

Looks like this one missed 6.0. Vinod, can you please merge this now?

Thanks,
Mani

> ---
> 
> Note: This patch is made on top of Frank and Serge's edma work, but should
> be applicable independently also.
> 
> [PATCH v10 0/9] Enable designware PCI EP EDMA locally
> [PATCH v2 00/26] dmaengine: dw-edma: Add RP/EP local DMA controllers support
> 
>  drivers/dma/dw-edma/dw-edma-core.c | 12 ------------
>  1 file changed, 12 deletions(-)
> 
> diff --git a/drivers/dma/dw-edma/dw-edma-core.c b/drivers/dma/dw-edma/dw-edma-core.c
> index 561686b51915..b2b5077d380b 100644
> --- a/drivers/dma/dw-edma/dw-edma-core.c
> +++ b/drivers/dma/dw-edma/dw-edma-core.c
> @@ -9,7 +9,6 @@
>  #include <linux/module.h>
>  #include <linux/device.h>
>  #include <linux/kernel.h>
> -#include <linux/pm_runtime.h>
>  #include <linux/dmaengine.h>
>  #include <linux/err.h>
>  #include <linux/interrupt.h>
> @@ -731,15 +730,12 @@ static int dw_edma_alloc_chan_resources(struct dma_chan *dchan)
>  		dchan->dev->chan_dma_dev = false;
>  	}
>  
> -	pm_runtime_get(chan->dw->chip->dev);
> -
>  	return 0;
>  }
>  
>  static void dw_edma_free_chan_resources(struct dma_chan *dchan)
>  {
>  	unsigned long timeout = jiffies + msecs_to_jiffies(5000);
> -	struct dw_edma_chan *chan = dchan2dw_edma_chan(dchan);
>  	int ret;
>  
>  	while (time_before(jiffies, timeout)) {
> @@ -752,8 +748,6 @@ static void dw_edma_free_chan_resources(struct dma_chan *dchan)
>  
>  		cpu_relax();
>  	}
> -
> -	pm_runtime_put(chan->dw->chip->dev);
>  }
>  
>  static int dw_edma_channel_setup(struct dw_edma *dw, u32 wr_alloc, u32 rd_alloc)
> @@ -1010,9 +1004,6 @@ int dw_edma_probe(struct dw_edma_chip *chip)
>  	if (err)
>  		goto err_irq_free;
>  
> -	/* Power management */
> -	pm_runtime_enable(dev);
> -
>  	/* Turn debugfs on */
>  	dw_edma_v0_core_debugfs_on(dw);
>  
> @@ -1046,9 +1037,6 @@ int dw_edma_remove(struct dw_edma_chip *chip)
>  	for (i = (dw->nr_irqs - 1); i >= 0; i--)
>  		free_irq(chip->ops->irq_vector(dev, i), &dw->irq[i]);
>  
> -	/* Power management */
> -	pm_runtime_disable(dev);
> -
>  	/* Deregister eDMA device */
>  	dma_async_device_unregister(&dw->dma);
>  	list_for_each_entry_safe(chan, _chan, &dw->dma.channels,
> -- 
> 2.25.1
> 

-- 
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