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

[Murali Karicheri <m-karicheri2-l0cyMroinI0@public.gmane.org>]

On 01/28/2015 10:45 AM, Rob Herring wrote:
> On Wed, Jan 28, 2015 at 5:05 AM, Catalin Marinas
> <catalin.marinas-5wv7dgnIgG8@public.gmane.org>  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;
>
> Are we assuming dma_addr, paddr and size are not touched on error? If
> so, we can get rid of this clause entirely.
Checking the code for of_dma_get_range() I see paddr is modified on 
error case, but is used only for success case in this function. dma_addr 
and size are not modified. So setting dma_addr and offset to zero before 
hand like size might work as below

dma_addr = offset = 0;
size = 1ULL <<  32;

ret = of_dma_get_range(dev->of_node,&dma_addr,&paddr,&size);
if (!ret) {
	offset = PFN_DOWN(paddr - dma_addr);
}

.. rest of the code.

Murali


>
>>          } 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;
>
> As I mentioned, I think power of 2 is too restrictive (from a DT
> perspective even though the kernel may require a power of 2 here for
> the mask). Just checking bit0 set should be enough.
>
> Also, we need a WARN here so DTs get fixed.
>
>> +
>> +       /*
>> +        * 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 ");
>>
>> --
>> Catalin


-- 
Murali Karicheri
Linux Kernel, Texas Instruments