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Subject: Re: [PATCH v1 07/10] powerpc/pseries/iommu: Allow DDW windows
 starting at 0x00
To:     Leonardo Bras <leobras.c@gmail.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Christophe Leroy <christophe.leroy@c-s.fr>,
        Joel Stanley <joel@jms.id.au>,
        Thiago Jung Bauermann <bauerman@linux.ibm.com>,
        Ram Pai <linuxram@us.ibm.com>,
        Brian King <brking@linux.vnet.ibm.com>,
        Murilo Fossa Vicentini <muvic@linux.ibm.com>,
        David Dai <zdai@linux.vnet.ibm.com>
Cc:     linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
References: <20200817234033.442511-1-leobras.c@gmail.com>
 <20200817234033.442511-8-leobras.c@gmail.com>
From:   Alexey Kardashevskiy <aik@ozlabs.ru>
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Message-ID: <3fda1c2d-20f2-7789-e072-47fe966f0265@ozlabs.ru>
Date:   Mon, 24 Aug 2020 13:44:08 +1000
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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@gmail.com>
> ---
>  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,


>  	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;
>  }
> 

-- 
Alexey