Re: [PATCH v5 05/11] powerpc/pseries/iommu: Allow DDW windows starting at 0x00

[Frederic Barrat <fbarrat@linux.ibm.com>]

On 16/07/2021 10:27, 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@gmail.com>
> Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> ---


Looks good to me
Reviewed-by: Frederic Barrat <fbarrat@linux.ibm.com>



>   arch/powerpc/platforms/pseries/iommu.c | 36 +++++++++++++-------------
>   1 file changed, 18 insertions(+), 18 deletions(-)
> 
> diff --git a/arch/powerpc/platforms/pseries/iommu.c b/arch/powerpc/platforms/pseries/iommu.c
> index 712d1667144a..b34b473bbdc1 100644
> --- a/arch/powerpc/platforms/pseries/iommu.c
> +++ b/arch/powerpc/platforms/pseries/iommu.c
> @@ -853,25 +853,26 @@ static void remove_ddw(struct device_node *np, bool remove_prop)
>   			np, ret);
>   }
>   
> -static u64 find_existing_ddw(struct device_node *pdn, int *window_shift)
> +static bool find_existing_ddw(struct device_node *pdn, u64 *dma_addr, int *window_shift)
>   {
>   	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);
>   			*window_shift = be32_to_cpu(direct64->window_shift);
> +			found = true;
>   			break;
>   		}
>   	}
>   	spin_unlock(&direct_window_list_lock);
>   
> -	return dma_addr;
> +	return found;
>   }
>   
>   static struct direct_window *ddw_list_new_entry(struct device_node *pdn,
> @@ -1161,20 +1162,20 @@ static int iommu_get_page_shift(u32 query_page_size)
>    * 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 = 0, ret;
>   	int max_ram_len = order_base_2(ddw_memory_hotplug_max());
>   	struct ddw_query_response query;
>   	struct ddw_create_response create;
>   	int page_shift;
> -	u64 dma_addr;
>   	struct device_node *dn;
>   	u32 ddw_avail[DDW_APPLICABLE_SIZE];
>   	struct direct_window *window;
>   	struct property *win64;
> +	bool ddw_enabled = false;
>   	struct dynamic_dma_window_prop *ddwprop;
>   	struct failed_ddw_pdn *fpdn;
>   	bool default_win_removed = false;
> @@ -1186,9 +1187,10 @@ static u64 enable_ddw(struct pci_dev *dev, struct device_node *pdn)
>   
>   	mutex_lock(&direct_window_init_mutex);
>   
> -	dma_addr = find_existing_ddw(pdn, &len);
> -	if (dma_addr != 0)
> +	if (find_existing_ddw(pdn, &dev->dev.archdata.dma_offset, &len)) {
> +		ddw_enabled = true;
>   		goto out_unlock;
> +	}
>   
>   	/*
>   	 * If we already went through this for a previous function of
> @@ -1342,7 +1344,8 @@ static u64 enable_ddw(struct pci_dev *dev, struct device_node *pdn)
>   	list_add(&window->list, &direct_window_list);
>   	spin_unlock(&direct_window_list_lock);
>   
> -	dma_addr = be64_to_cpu(ddwprop->dma_base);
> +	dev->dev.archdata.dma_offset = be64_to_cpu(ddwprop->dma_base);
> +	ddw_enabled = true;
>   	goto out_unlock;
>   
>   out_free_window:
> @@ -1374,10 +1377,10 @@ static u64 enable_ddw(struct pci_dev *dev, struct device_node *pdn)
>   	 * as RAM, then we failed to create a window to cover persistent
>   	 * memory and need to set the DMA limit.
>   	 */
> -	if (pmem_present && dma_addr && (len == max_ram_len))
> -		dev->dev.bus_dma_limit = dma_addr + (1ULL << len);
> +	if (pmem_present && ddw_enabled && (len == max_ram_len))
> +		dev->dev.bus_dma_limit = dev->dev.archdata.dma_offset + (1ULL << len);
>   
> -	return dma_addr;
> +	return ddw_enabled;
>   }
>   
>   static void pci_dma_dev_setup_pSeriesLP(struct pci_dev *dev)
> @@ -1456,11 +1459,8 @@ 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;
>   }
>