linux-kernel - Re: [PATCH kernel v3 2/2] powerpc/dma: Fallback to dma

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Date:   Thu, 29 Oct 2020 20:55:33 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Alexey Kardashevskiy <aik@...abs.ru>, linuxppc-dev@...ts.ozlabs.org
Cc:     Christoph Hellwig <hch@....de>, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH kernel v3 2/2] powerpc/dma: Fallback to dma_ops when persistent memory present

Alexey Kardashevskiy <aik@...abs.ru> writes:
> On 29/10/2020 11:40, Michael Ellerman wrote:
>> Alexey Kardashevskiy <aik@...abs.ru> writes:
>>> @@ -1126,7 +1129,7 @@ static u64 enable_ddw(struct pci_dev *dev, struct device_node *pdn)
>>>   
>>>   	mutex_lock(&direct_window_init_mutex);
>>>   
>>> -	dma_addr = find_existing_ddw(pdn);
>>> +	dma_addr = find_existing_ddw(pdn, &len);
>> 
>> I don't see len used anywhere?
>> 
>>>   	if (dma_addr != 0)
>>>   		goto out_unlock;
>>>   
>>> @@ -1212,14 +1215,26 @@ static u64 enable_ddw(struct pci_dev *dev, struct device_node *pdn)
>>>   	}
>>>   	/* verify the window * number of ptes will map the partition */
>>>   	/* check largest block * page size > max memory hotplug addr */
>>> -	max_addr = ddw_memory_hotplug_max();
>>> -	if (query.largest_available_block < (max_addr >> page_shift)) {
>>> -		dev_dbg(&dev->dev, "can't map partition max 0x%llx with %llu "
>>> -			  "%llu-sized pages\n", max_addr,  query.largest_available_block,
>>> -			  1ULL << page_shift);
>>> +	/*
>>> +	 * The "ibm,pmemory" can appear anywhere in the address space.
>>> +	 * Assuming it is still backed by page structs, try MAX_PHYSMEM_BITS
>>> +	 * for the upper limit and fallback to max RAM otherwise but this
>>> +	 * disables device::dma_ops_bypass.
>>> +	 */
>>> +	len = max_ram_len;
>> 
>> Here you override whatever find_existing_ddw() wrote to len?
>
> Not always, there is a bunch of gotos before this line to the end of the 
> function and one (which returns the existing window) is legit. Thanks,

Ah yep I see it.

Gotos considered confusing ;)

cheers