Re: [PATCH v1 07/10] powerpc/pseries/iommu: Allow DDW windows starting at 0x00

[Leonardo Bras]

On Mon, 2020-08-24 at 13:44 +1000, Alexey Kardashevskiy wrote:
> 
> > On 18/08/2020 09:40, Leonardo Bras wrote:
> > enable_ddw() currently returns the address of the DMA window, which is
> > considered invalid if has the value 0x00.
> > 
> > Also, it only considers valid an address returned from find_existing_ddw
> > if it's not 0x00.
> > 
> > Changing this behavior makes sense, given the users of enable_ddw() only
> > need to know if direct mapping is possible. It can also allow a DMA window
> > starting at 0x00 to be used.
> > 
> > This will be helpful for using a DDW with indirect mapping, as the window
> > address will be different than 0x00, but it will not map the whole
> > partition.
> > 
> > Signed-off-by: Leonardo Bras <leobras.c@xxxxxxxxx>
> > ---
> >  arch/powerpc/platforms/pseries/iommu.c | 30 ++++++++++++--------------
> >  1 file changed, 14 insertions(+), 16 deletions(-)
> > 
> > diff --git a/arch/powerpc/platforms/pseries/iommu.c b/arch/powerpc/platforms/pseries/iommu.c
> > index fcdefcc0f365..4031127c9537 100644
> > --- a/arch/powerpc/platforms/pseries/iommu.c
> > +++ b/arch/powerpc/platforms/pseries/iommu.c
> > @@ -852,24 +852,25 @@ static void remove_ddw(struct device_node *np, bool remove_prop)
> >  			np, ret);
> >  }
> > >  
> > -static u64 find_existing_ddw(struct device_node *pdn)
> > +static bool find_existing_ddw(struct device_node *pdn, u64 *dma_addr)
> >  {
> >  	struct direct_window *window;
> >  	const struct dynamic_dma_window_prop *direct64;
> > -	u64 dma_addr = 0;
> > +	bool found = false;
> >  
> >  	spin_lock(&direct_window_list_lock);
> >  	/* check if we already created a window and dupe that config if so */
> >  	list_for_each_entry(window, &direct_window_list, list) {
> >  		if (window->device == pdn) {
> >  			direct64 = window->prop;
> > -			dma_addr = be64_to_cpu(direct64->dma_base);
> > +			*dma_addr = be64_to_cpu(direct64->dma_base);
> > +			found = true;
> >  			break;
> >  		}
> >  	}
> >  	spin_unlock(&direct_window_list_lock);
> >  
> > -	return dma_addr;
> > +	return found;
> >  }
> >  
> >  static struct direct_window *ddw_list_add(struct device_node *pdn,
> > @@ -1131,15 +1132,15 @@ static void reset_dma_window(struct pci_dev *dev, struct device_node *par_dn)
> >   * pdn: the parent pe node with the ibm,dma_window property
> >   * Future: also check if we can remap the base window for our base page size
> >   *
> > - * returns the dma offset for use by the direct mapped DMA code.
> > + * returns true if can map all pages (direct mapping), false otherwise..
> >   */
> > -static u64 enable_ddw(struct pci_dev *dev, struct device_node *pdn)
> > +static bool enable_ddw(struct pci_dev *dev, struct device_node *pdn)
> >  {
> >  	int len, ret;
> >  	struct ddw_query_response query;
> >  	struct ddw_create_response create;
> >  	int page_shift;
> > -	u64 dma_addr, max_addr;
> > +	u64 max_addr;
> >  	struct device_node *dn;
> >  	u32 ddw_avail[DDW_APPLICABLE_SIZE];
> >  	struct direct_window *window;
> > @@ -1150,8 +1151,7 @@ static u64 enable_ddw(struct pci_dev *dev, struct device_node *pdn)
> >  
> >  	mutex_lock(&direct_window_init_mutex);
> >  
> > -	dma_addr = find_existing_ddw(pdn);
> > -	if (dma_addr != 0)
> > +	if (find_existing_ddw(pdn, &dev->dev.archdata.dma_offset))
> >  		goto out_unlock;
> >  
> >  	/*
> > @@ -1292,7 +1292,7 @@ static u64 enable_ddw(struct pci_dev *dev, struct device_node *pdn)
> >  		goto out_free_window;
> >  	}
> >  
> > -	dma_addr = be64_to_cpu(ddwprop->dma_base);
> > +	dev->dev.archdata.dma_offset = be64_to_cpu(ddwprop->dma_base);
> 
> Do not you need the same chunk in the find_existing_ddw() case above as
> well? Thanks,

The new signature of find_existing_ddw() is 
static bool find_existing_ddw(struct device_node *pdn, u64 *dma_addr)

And on enable_ddw(), we call 
find_existing_ddw(pdn, &dev->dev.archdata.dma_offset)

And inside the function we do:
*dma_addr = be64_to_cpu(direct64->dma_base);

I think it's the same as the chunk before.
Am I missing something?

> 
> 
> >  	goto out_unlock;
> >  
> >  out_free_window:
> > @@ -1309,6 +1309,7 @@ static u64 enable_ddw(struct pci_dev *dev, struct device_node *pdn)
> >  	kfree(win64->name);
> >  	kfree(win64->value);
> >  	kfree(win64);
> > +	win64 = NULL;
> >  
> >  out_failed:
> >  	if (default_win_removed)
> > @@ -1322,7 +1323,7 @@ static u64 enable_ddw(struct pci_dev *dev, struct device_node *pdn)
> >  
> >  out_unlock:
> >  	mutex_unlock(&direct_window_init_mutex);
> > -	return dma_addr;
> > +	return win64;
> >  }
> >  
> >  static void pci_dma_dev_setup_pSeriesLP(struct pci_dev *dev)
> > @@ -1401,11 +1402,8 @@ static bool iommu_bypass_supported_pSeriesLP(struct pci_dev *pdev, u64 dma_mask)
> >  			break;
> >  	}
> >  
> > -	if (pdn && PCI_DN(pdn)) {
> > -		pdev->dev.archdata.dma_offset = enable_ddw(pdev, pdn);
> > -		if (pdev->dev.archdata.dma_offset)
> > -			return true;
> > -	}
> > +	if (pdn && PCI_DN(pdn))
> > +		return enable_ddw(pdev, pdn);
> >  
> >  	return false;
> >  }
> >