linux-kernel - Re: [PATCH v4 3/6] of: fix size when dma-range is not used

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Message-ID: <54C7DF13.20402@ti.com>
Date:	Tue, 27 Jan 2015 13:55:15 -0500
From:	Murali Karicheri <m-karicheri2@...com>
To:	Robin Murphy <robin.murphy@....com>
CC:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	Russell King <linux@....linux.org.uk>,
	Arnd Bergmann <arnd@...db.de>, Joerg Roedel <joro@...tes.org>,
	Will Deacon <Will.Deacon@....com>,
	Rob Herring <robh+dt@...nel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	"suravee.suthikulpanit@....com" <suravee.suthikulpanit@....com>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>
Subject: Re: [PATCH v4 3/6] of: fix size when dma-range is not used

On 01/27/2015 06:27 AM, Robin Murphy wrote:
> Hi Murali,
>
> On 23/01/15 22:32, Murali Karicheri wrote:
>> Fix the dma-range size when the DT attribute is missing. i.e set size to
>> dev->coherent_dma_mask + 1 instead of dev->coherent_dma_mask. To detect
>> overflow when mask is set to max of u64, add a check, log error and
>> return.
>> Some platform use mask format for size in DTS. So add a work around to
>> catch this and fix.
>>
>> Cc: Joerg Roedel <joro@...tes.org>
>> Cc: Grant Likely <grant.likely@...aro.org>
>> Cc: Rob Herring <robh+dt@...nel.org>
>> Cc: Bjorn Helgaas <bhelgaas@...gle.com>
>> Cc: Will Deacon <will.deacon@....com>
>> Cc: Russell King <linux@....linux.org.uk>
>> Cc: Arnd Bergmann <arnd@...db.de>
>> Cc: Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
>>
>> Signed-off-by: Murali Karicheri <m-karicheri2@...com>
>> ---
>> drivers/of/device.c | 14 +++++++++++++-
>> 1 file changed, 13 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/of/device.c b/drivers/of/device.c
>> index 2de320d..0a5ff54 100644
>> --- a/drivers/of/device.c
>> +++ b/drivers/of/device.c
>> @@ -105,12 +105,24 @@ void of_dma_configure(struct device *dev, struct
>> device_node *np)
>> ret = of_dma_get_range(np, &dma_addr, &paddr, &size);
>> if (ret < 0) {
>> dma_addr = offset = 0;
>> - size = dev->coherent_dma_mask;
>> + size = dev->coherent_dma_mask + 1;
>> } else {
>> offset = PFN_DOWN(paddr - dma_addr);
>> + /*
>> + * Add a work around to treat the size as mask + 1 in case
>> + * it is defined in DT as a mask.
>> + */
>> + if (size & 1)
>> + size = size + 1;
>> dev_dbg(dev, "dma_pfn_offset(%#08lx)\n", offset);
>> }
>>
>> + /* if size is 0, we have an overflow of u64 */
>> + if (!size) {
>> + dev_err(dev, "invalid size\n");
>> + return;
>> + }
>> +
>
> This seems potentially fragile to dodgy DTs given that we might also be
> using size to make a mask later. Would it make sense to double-up a
> sanity check as mask-format detection? Something like:
>
> if is_power_of_2(size)
> // use size
> else if is_power_of_2(size + 1)
> // use size + 1
> else
> // cry
Robin,

How about having the logic like this?

	ret = of_dma_get_range(np, &dma_addr, &paddr, &size);
	if (ret < 0) {
		dma_addr = offset = 0;
		size = dev->coherent_dma_mask + 1;
	} else {
		offset = PFN_DOWN(paddr - dma_addr);
		dev_dbg(dev, "dma_pfn_offset(%#08lx)\n", offset);
	}

	if (is_power_of_2(size + 1))
		size = size + 1;
	else if (!is_power_of_2(size))
	{
		dev_err(dev, "invalid size\n");
		return;
	}

Murali
>
>
> Robin.
>
>> dev->dma_pfn_offset = offset;
>>
>> coherent = of_dma_is_coherent(np);
>>
>
>


-- 
Murali Karicheri
Linux Kernel, Texas Instruments
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