Re: [PATCH kernel RFC 1/3] powerpc/pseries/iommu: Allow dynamic window to start from zero

[David Gibson <david@gibson.dropbear.id.au>]

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On Wed, Jul 25, 2018 at 07:50:30PM +1000, Alexey Kardashevskiy wrote:
> At the moment the kernel does not expect dynamic windows to ever start
> at zero on a PCI bus as PAPR requires the hypervisor to create a 32bit
> default window which starts from zero and the pseries kernel only
> creates additional windows.
> 
> However PAPR permits removing the default window and creating another
> one instead, starting from zero as well. In fact, the kernel used to
> remove the default window after sha1 25ebc45b934 but this has been
> reverted later.
> 
> Since there are devices capable of more than 32 bits for DMA but less than
> 50, and currently available hardware allows the second window only
> at 1<<59, we will need to be able to create bigger windows starting from
> zero. This does the initial preparation and should not cause any
> behavioral changes.
> 
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

> ---
>  arch/powerpc/platforms/pseries/iommu.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/powerpc/platforms/pseries/iommu.c b/arch/powerpc/platforms/pseries/iommu.c
> index 06f0296..9ece42f 100644
> --- a/arch/powerpc/platforms/pseries/iommu.c
> +++ b/arch/powerpc/platforms/pseries/iommu.c
> @@ -53,6 +53,8 @@
>  
>  #include "pseries.h"
>  
> +#define DDW_INVALID_OFFSET	((uint64_t)-1)
> +
>  static struct iommu_table_group *iommu_pseries_alloc_group(int node)
>  {
>  	struct iommu_table_group *table_group;
> @@ -844,7 +846,7 @@ static u64 find_existing_ddw(struct device_node *pdn)
>  {
>  	struct direct_window *window;
>  	const struct dynamic_dma_window_prop *direct64;
> -	u64 dma_addr = 0;
> +	u64 dma_addr = DDW_INVALID_OFFSET;
>  
>  	spin_lock(&direct_window_list_lock);
>  	/* check if we already created a window and dupe that config if so */
> @@ -992,7 +994,7 @@ 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 (dma_addr != DDW_INVALID_OFFSET)
>  		goto out_unlock;
>  
>  	/*
> @@ -1228,7 +1230,7 @@ static int dma_set_mask_pSeriesLP(struct device *dev, u64 dma_mask)
>  		}
>  		if (pdn && PCI_DN(pdn)) {
>  			dma_offset = enable_ddw(pdev, pdn);
> -			if (dma_offset != 0) {
> +			if (dma_offset != DDW_INVALID_OFFSET) {
>  				dev_info(dev, "Using 64-bit direct DMA at offset %llx\n", dma_offset);
>  				set_dma_offset(dev, dma_offset);
>  				set_dma_ops(dev, &dma_nommu_ops);

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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