Re: [PATCH v4 4/7] powerpc/pseries/iommu: Remove default DMA window before creating DDW

[David Dai]

On Thu, 2020-07-16 at 04:16 -0300, Leonardo Bras wrote:
> On LoPAR "DMA Window Manipulation Calls", it's recommended to remove
> the
> default DMA window for the device, before attempting to configure a
> DDW,
> in order to make the maximum resources available for the next DDW to
> be
> created.
> 
> This is a requirement for using DDW on devices in which hypervisor
> allows only one DMA window.
> 
> If setting up a new DDW fails anywhere after the removal of this
> default DMA window, it's needed to restore the default DMA window.
> For this, an implementation of ibm,reset-pe-dma-windows rtas call is
> needed:
> 
> Platforms supporting the DDW option starting with LoPAR level 2.7
> implement
> ibm,ddw-extensions. The first extension available (index 2) carries
> the
> token for ibm,reset-pe-dma-windows rtas call, which is used to
> restore
> the default DMA window for a device, if it has been deleted.
> 
> It does so by resetting the TCE table allocation for the PE to it's
> boot time value, available in "ibm,dma-window" device tree node.
> 
> Signed-off-by: Leonardo Bras <leobras.c@xxxxxxxxx>
> ---
>  arch/powerpc/platforms/pseries/iommu.c | 73 +++++++++++++++++++++++-
> --
>  1 file changed, 66 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/powerpc/platforms/pseries/iommu.c
> b/arch/powerpc/platforms/pseries/iommu.c
> index 4e33147825cc..fc8d0555e2e9 100644
> --- a/arch/powerpc/platforms/pseries/iommu.c
> +++ b/arch/powerpc/platforms/pseries/iommu.c
> @@ -1066,6 +1066,38 @@ static phys_addr_t
> ddw_memory_hotplug_max(void)
>  	return max_addr;
>  }
>  
> +/*
> + * Platforms supporting the DDW option starting with LoPAR level 2.7
> implement
> + * ibm,ddw-extensions, which carries the rtas token for
> + * ibm,reset-pe-dma-windows.
> + * That rtas-call can be used to restore the default DMA window for
> the device.
> + */
> +static void reset_dma_window(struct pci_dev *dev, struct device_node
> *par_dn)
> +{
> +	int ret;
> +	u32 cfg_addr, reset_dma_win;
> +	u64 buid;
> +	struct device_node *dn;
> +	struct pci_dn *pdn;
> +
> +	ret = ddw_read_ext(par_dn, DDW_EXT_RESET_DMA_WIN,
> &reset_dma_win);
> +	if (ret)
> +		return;
> +
> +	dn = pci_device_to_OF_node(dev);
> +	pdn = PCI_DN(dn);
> +	buid = pdn->phb->buid;
> +	cfg_addr = ((pdn->busno << 16) | (pdn->devfn << 8));
> +
> +	ret = rtas_call(reset_dma_win, 3, 1, NULL, cfg_addr,
> BUID_HI(buid),
> +			BUID_LO(buid));
> +	if (ret)
> +		dev_info(&dev->dev,
> +			 "ibm,reset-pe-dma-windows(%x) %x %x %x
> returned %d ",
> +			 reset_dma_win, cfg_addr, BUID_HI(buid),
> BUID_LO(buid),
> +			 ret);
> +}
> +
>  /*
>   * If the PE supports dynamic dma windows, and there is space for a
> table
>   * that can map all pages in a linear offset, then setup such a
> table,
> @@ -1090,6 +1122,7 @@ static u64 enable_ddw(struct pci_dev *dev,
> struct device_node *pdn)
>  	struct property *win64;
>  	struct dynamic_dma_window_prop *ddwprop;
>  	struct failed_ddw_pdn *fpdn;
> +	bool default_win_removed = false;
>  
>  	mutex_lock(&direct_window_init_mutex);
>  
> @@ -1133,14 +1166,38 @@ static u64 enable_ddw(struct pci_dev *dev,
> struct device_node *pdn)
>  	if (ret != 0)
>  		goto out_failed;
>  
> +	/*
> +	 * If there is no window available, remove the default DMA
> window,
> +	 * if it's present. This will make all the resources available
> to the
> +	 * new DDW window.
> +	 * If anything fails after this, we need to restore it, so also
> check
> +	 * for extensions presence.
> +	 */
>  	if (query.windows_available == 0) {
> -		/*
> -		 * no additional windows are available for this device.
> -		 * We might be able to reallocate the existing window,
> -		 * trading in for a larger page size.
> -		 */
> -		dev_dbg(&dev->dev, "no free dynamic windows");
> -		goto out_failed;
> +		struct property *default_win;
> +		int reset_win_ext;
> +
> +		default_win = of_find_property(pdn, "ibm,dma-window",
> NULL);
> +		if (!default_win)
> +			goto out_failed;
> +
> +		reset_win_ext = ddw_read_ext(pdn,
> DDW_EXT_RESET_DMA_WIN, NULL);
> +		if (reset_win_ext)
> +			goto out_failed;
> +
> +		remove_dma_window(pdn, ddw_avail, default_win);
> +		default_win_removed = true;
> +
> +		/* Query again, to check if the window is available */
> +		ret = query_ddw(dev, ddw_avail, &query, pdn);
> +		if (ret != 0)
> +			goto out_failed;
> +
> +		if (query.windows_available == 0) {
> +			/* no windows are available for this device. */
> +			dev_dbg(&dev->dev, "no free dynamic windows");
> +			goto out_failed;
> +		}
>  	}
>  	if (query.page_size & 4) {
>  		page_shift = 24; /* 16MB */
> @@ -1231,6 +1288,8 @@ static u64 enable_ddw(struct pci_dev *dev,
> struct device_node *pdn)
>  	kfree(win64);
>  
>  out_failed:
> +	if (default_win_removed)
> +		reset_dma_window(dev, pdn);
>  
>  	fpdn = kzalloc(sizeof(*fpdn), GFP_KERNEL);
>  	if (!fpdn)
Tested-by: David Dai <zdai@xxxxxxxxxxxxxxxxxx>