linux-kernel - RE: [PATCH v2 2/2] drivers: remove force dma flag from buses

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Date:   Thu, 22 Mar 2018 15:13:49 +0000
From:   Nipun Gupta <nipun.gupta@....com>
To:     Christoph Hellwig <hch@....de>
CC:     "robin.murphy@....com" <robin.murphy@....com>,
        "linux@...linux.org.uk" <linux@...linux.org.uk>,
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        Bharat Bhushan <bharat.bhushan@....com>,
        Leo Li <leoyang.li@....com>
Subject: RE: [PATCH v2 2/2] drivers: remove force dma flag from buses



> -----Original Message-----
> From: Christoph Hellwig [mailto:hch@....de]
> Sent: Thursday, March 22, 2018 13:49
> To: Nipun Gupta <nipun.gupta@....com>
> 
> > --- a/drivers/dma/qcom/hidma_mgmt.c
> > +++ b/drivers/dma/qcom/hidma_mgmt.c
> > @@ -398,7 +398,7 @@ static int __init
> hidma_mgmt_of_populate_channels(struct device_node *np)
> >  		}
> >  		of_node_get(child);
> >  		new_pdev->dev.of_node = child;
> > -		of_dma_configure(&new_pdev->dev, child);
> > +		of_dma_configure(&new_pdev->dev, child, true);
> >  		/*
> >  		 * It is assumed that calling of_msi_configure is safe on
> >  		 * platforms with or without MSI support.
> 
> Where did we mark this bus as force_dma before?

I thought these devices to be on the platform bus as the device is of type
'struct platform_device', though I am not sure then why 'of_dma_configure()'
is called here. Is this not on platform bus?

> 
> > diff --git a/drivers/of/of_reserved_mem.c b/drivers/of/of_reserved_mem.c
> > index 9a4f4246..895c83e 100644
> > --- a/drivers/of/of_reserved_mem.c
> > +++ b/drivers/of/of_reserved_mem.c
> > @@ -353,7 +353,7 @@ int of_reserved_mem_device_init_by_idx(struct device
> *dev,
> >  		/* ensure that dma_ops is set for virtual devices
> >  		 * using reserved memory
> >  		 */
> > -		of_dma_configure(dev, np);
> > +		of_dma_configure(dev, np, true);
> 
> Did all the callers of this one really force dma?  I have a hard time
> untangling the call stacks unfortunately.

I see this API being called indirectly from NXP DPAA device driver which
is for platform bus devices. So I marked 'true' out here. There are more places
from where it is being called.

Thanks,
Nipun