linux-kernel - Re: [PATCH 1/2] dma-mapping: let arch know origin of dma range passed to arch_setup_dma

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Date:   Thu, 12 Jan 2017 08:52:51 +0300
From:   Nikita Yushchenko <nikita.yoush@...entembedded.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Robin Murphy <robin.murphy@....com>,
        Will Deacon <will.deacon@....com>,
        linux-arm-kernel@...ts.infradead.org,
        linux-renesas-soc@...r.kernel.org,
        Simon Horman <horms@...ge.net.au>,
        Bjorn Helgaas <bhelgaas@...gle.com>, fkan@....com,
        linux-kernel@...r.kernel.org,
        Artemi Ivanov <artemi.ivanov@...entembedded.com>
Subject: Re: [PATCH 1/2] dma-mapping: let arch know origin of dma range passed
 to arch_setup_dma_ops()

>> diff --git a/drivers/staging/fsl-mc/bus/fsl-mc-bus.c b/drivers/staging/fsl-mc/bus/fsl-mc-bus.c
>> index 5ac373c..480b644 100644
>> --- a/drivers/staging/fsl-mc/bus/fsl-mc-bus.c
>> +++ b/drivers/staging/fsl-mc/bus/fsl-mc-bus.c
>> @@ -540,7 +540,7 @@ int fsl_mc_device_add(struct dprc_obj_desc *obj_desc,
>>  
>>  	/* Objects are coherent, unless 'no shareability' flag set. */
>>  	if (!(obj_desc->flags & DPRC_OBJ_FLAG_NO_MEM_SHAREABILITY))
>> -		arch_setup_dma_ops(&mc_dev->dev, 0, 0, NULL, true);
>> +		arch_setup_dma_ops(&mc_dev->dev, 0, 0, false, NULL, true);
>>  
>>  	/*
>>  	 * The device-specific probe callback will get invoked by device_add()
> 
> Why are these actually calling arch_setup_dma_ops() here in the first
> place? Are these all devices that are DMA masters without an OF node?

I don't know, but that's a different topic. This patch just adds
argument and sets it to false everywhere but in the location when range
should be definitely enforced.

>> @@ -126,6 +127,8 @@ void of_dma_configure(struct device *dev, struct device_node *np)
>>  			return;
>>  		}
>>  		dev_dbg(dev, "dma_pfn_offset(%#08lx)\n", offset);
>> +
>> +		enforce_range = true;
>>  	}
>>  
>>  	dev->dma_pfn_offset = offset;
> 
> Hmm, I think when the dma-ranges are missing, we should either enforce
> a 32-bit mask, or disallow DMA completely. It's probably too late for
> the latter, I wish we had done this earlier in order to force everyone
> on ARM64 to have a valid dma-ranges property for any DMA master.

This can be done over time.

However the very idea of this version of patch is - keep working pieces
as-is, thus for now setting enforce_range to false in case of no defined
dma-ranges is intentional.

What I should re-check is - does rcar dtsi set dma-ranges, and add it if
it does not.

Nikita