Le 17/11/2016 à 13:21, Harini Katakam a écrit :
> Hi Rafal,
>
> On Thu, Nov 17, 2016 at 5:20 PM, Rafal Ozieblo <raf...@cadence.com> wrote:
>> Hello,
>> I think, there could a bug in your patch.
>>
>>> +
>>> +#ifdef CONFIG_ARCH_DMA_ADDR_T_64BIT
>>> + dmacfg |= GEM_BIT(ADDR64);
>>> +#endif
>>
>> You enable 64 bit addressing (64b dma bus width) always when appropriate
>> architecture config option is enabled.
>> But there are some legacy controllers which do not support that feature.
>> According Cadence hardware team:
>> "64 bit addressing was added in July 2013. Earlier version do not have it.
>> This feature was enhanced in release August 2014 to have separate upper
>> address values for transmit and receive."
>>
>>> /* Bitfields in NSR */
>>> @@ -474,6 +479,10 @@
>>> struct macb_dma_desc {
>> > u32 addr;
>>> u32 ctrl;
>>> +#ifdef CONFIG_ARCH_DMA_ADDR_T_64BIT
>>> + u32 addrh;
>>> + u32 resvd;
>>> +#endif
>>> };
>>
>> It will not work for legacy hardware. Old descriptor is 2 words wide, the
>> new one is 4 words wide.
>> If you enable CONFIG_ARCH_DMA_ADDR_T_64BIT but hardware doesn't support it
>> at all,
>> you will miss every second descriptor.
>>
>
> True, this feature is not available in all of Cadence IP versions.
> In fact, the IP version Zynq does not support this. But the one in ZynqMP
> does.
> So, we enable kernel config for 64 bit DMA addressing for this SoC and hence
> the driver picks it up. My assumption was that if the legacy IP does not
> support
> 64 bit addressing, then this DMA option wouldn't be enabled.
>
> There is a design config register in Cadence IP which is being read to
> check for 64 bit address support - DMA mask is set based on that.
> But the addition of two descriptor words cannot be based on this runtime
> check.
> For this reason, all the static changes were placed under this check.
We have quite a bunch of options in this driver to determinate what is
the real capacity of the underlying hardware.
If HW configuration registers are not appropriate, and it seems they are
not, I would advice to simply use the DT compatibility string.
Best regards,
--
Nicolas Ferre
