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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>
References: <20200817234033.442511-1-leobras.c@gmail.com>
 <20200817234033.442511-8-leobras.c@gmail.com>
 <3fda1c2d-20f2-7789-e072-47fe966f0265@ozlabs.ru>
 <2d2b1a048faf75c8e68f95b3bf2d9514721786c6.camel@gmail.com>
From: Alexey Kardashevskiy <aik@ozlabs.ru>
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On 29/08/2020 00:04, Leonardo Bras wrote:
> 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@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,
> 
> 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?

ah no, sorry, you are not missing anything.


Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>




-- 
Alexey