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

[Robin Murphy <robin.murphy-5wv7dgnIgG8@public.gmane.org>]

On 28/01/15 11:05, Catalin Marinas wrote:
> On Tue, Jan 27, 2015 at 06:55:15PM +0000, Murali Karicheri wrote:
>> On 01/27/2015 06:27 AM, Robin Murphy wrote:
>>> 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-zLv9SwRftAIdnm+yROfE0A@public.gmane.org>
>>>> Cc: Grant Likely <grant.likely-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
>>>> Cc: Rob Herring <robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
>>>> Cc: Bjorn Helgaas <bhelgaas-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
>>>> Cc: Will Deacon <will.deacon-5wv7dgnIgG8@public.gmane.org>
>>>> Cc: Russell King <linux-lFZ/pmaqli7XmaaqVzeoHQ@public.gmane.org>
>>>> Cc: Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org>
>>>> Cc: Suravee Suthikulpanit <Suravee.Suthikulpanit-5C7GfCeVMHo@public.gmane.org>
>>>>
>>>> Signed-off-by: Murali Karicheri <m-karicheri2-l0cyMroinI0@public.gmane.org>
>>>> ---
>>>> 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
>>
>> 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;
>> 	}
>
> In of_dma_configure(), we currently assume that the default coherent
> mask is 32-bit. In this thread:
>
> http://article.gmane.org/gmane.linux.kernel/1835096
>
> we talked about setting the coherent mask based on size automatically.
> I'm not sure about the size but I think we can assume is 32-bit mask + 1
> if it is not specified in the DT. Instead of just assuming a default
> mask, let's assume a default size and create the mask based on this
> (untested):
>
> diff --git a/drivers/of/platform.c b/drivers/of/platform.c
> index 5b33c6a21807..9ff8d1286b44 100644
> --- a/drivers/of/platform.c
> +++ b/drivers/of/platform.c
> @@ -170,10 +170,10 @@ static void of_dma_configure(struct device *dev)
>   	struct iommu_ops *iommu;
>
>   	/*
> -	 * Set default dma-mask to 32 bit. Drivers are expected to setup
> -	 * the correct supported dma_mask.
> +	 * Set default size to cover the 32-bit. Drivers are expected to setup
> +	 * the correct size and dma_mask.
>   	 */
> -	dev->coherent_dma_mask = DMA_BIT_MASK(32);
> +	size = 1ULL << 32;
>
>   	/*
>   	 * Set it to coherent_dma_mask by default if the architecture
> @@ -185,13 +185,24 @@ static void of_dma_configure(struct device *dev)
>   	ret = of_dma_get_range(dev->of_node, &dma_addr, &paddr, &size);
>   	if (ret < 0) {
>   		dma_addr = offset = 0;
> -		size = dev->coherent_dma_mask;
>   	} else {
>   		offset = PFN_DOWN(paddr - dma_addr);
>   		dev_dbg(dev, "dma_pfn_offset(%#08lx)\n", dev->dma_pfn_offset);
>   	}
>   	dev->dma_pfn_offset = offset;
>
> +	/*
> +	 * Workaround for DTs setting the size to a mask or 0.
> +	 */
> +	if (is_power_of_2(size + 1))
> +		size += 1;

In fact, since the ilog2 below ends up effectively rounding down, we 
might as well do away with this check as well and just add 1 
unconditionally. The only time it makes any difference is when we want 
it to anyway!

I like this approach, it ends up looking a lot neater.

Robin.

> +
> +	/*
> +	 * Coherent DMA masks larger than 32-bit must be explicitly set by the
> +	 * driver.
> +	 */
> +	dev->coherent_dma_mask = min(DMA_BIT_MASK(32), DMA_BIT_MASK(ilog2(size)));
> +
>   	coherent = of_dma_is_coherent(dev->of_node);
>   	dev_dbg(dev, "device is%sdma coherent\n",
>   		coherent ? " " : " not ");
>