Subject: [PATCH 1/2] DMA: fix AMBA PL08x driver issue with 64bit DMA address type

From: [email-masked] (Andre Przywara)
Date: Thu, 15 Aug 2013 23:07:26 +0200

On 08/14/2013 09:13 PM, Rob Herring wrote:
> On Wed, Aug 14, 2013 at 8:00 AM, Russell King - ARM Linux
> <[email-masked]> wrote:
>> NAK.
>
> This patch has nothing to do with dma masks or your dma mask series.
> The code deals with bus alignment and cleans up the code to do
> alignment operations in a sane way compared to modulo operator. The
> only thing 64-bit dma_addr_t did was expose crap code.

I agree. Actually I'd see the DMA mask thing just as an opportunity to 
fix this code, not as the reason. I guess there are gazillions of 
drivers in the ARM world which have problems with any address related 
variable being bigger than 32bit, and those should all be fixed eventually.

> Perhaps bus_addr_offset needs a better name to indicate it is dealing
> with bus alignment rather than bus address offset.

Actually my first patch version called this function 
unaligned_bus_addr(), but this was rather odd with the one non-boolean 
usage of it - where it actually wants to know the offset.

Regards,
Andre.

>> On Wed, Aug 14, 2013 at 02:52:08PM +0200, Andre Przywara wrote:
>>> In Rob's recent pull request the patch
>>>        ARM: highbank: select ARCH_DMA_ADDR_T_64BIT for LPAE
>>> promotes dma_addr_t to 64bit, which breaks compilation of the
>>> AMBA PL08x DMA driver.
>>> GCC has no function for the 64bit/8bit modulo operation.
>>> Looking more closely the divisor can only be 1, 2 or 4, so the full
>>> featured '%' modulo operation is overkill and can be replaced by
>>> simple bit masking.
>>>
>>> Signed-off-by: Andre Przywara <[email-masked]>
>>> ---
>>>   drivers/dma/amba-pl08x.c | 16 ++++++++++------
>>>   1 file changed, 10 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/drivers/dma/amba-pl08x.c b/drivers/dma/amba-pl08x.c
>>> index 06fe45c..29e1cf9 100644
>>> --- a/drivers/dma/amba-pl08x.c
>>> +++ b/drivers/dma/amba-pl08x.c
>>> @@ -286,6 +286,11 @@ static inline struct pl08x_txd *to_pl08x_txd(struct dma_async_tx_descriptor *tx)
>>>        return container_of(tx, struct pl08x_txd, vd.tx);
>>>   }
>>>
>>> +static int bus_addr_offset(struct pl08x_bus_data *bus)
>>> +{
>>> +     return bus->addr & (bus->buswidth - 1);
>>> +}
>>> +
>>>   /*
>>>    * Mux handling.
>>>    *
>>> @@ -886,8 +891,8 @@ static int pl08x_fill_llis_for_desc(struct pl08x_driver_data *pl08x,
>>>                                return 0;
>>>                        }
>>>
>>> -                     if ((bd.srcbus.addr % bd.srcbus.buswidth) ||
>>> -                                     (bd.dstbus.addr % bd.dstbus.buswidth)) {
>>> +                     if (bus_addr_offset(&bd.srcbus) ||
>>> +                                     bus_addr_offset(&bd.dstbus)) {
>>>                                dev_err(&pl08x->adev->dev,
>>>                                        "%s src & dst address must be aligned to src"
>>>                                        " & dst width if peripheral is flow controller",
>>> @@ -908,9 +913,8 @@ static int pl08x_fill_llis_for_desc(struct pl08x_driver_data *pl08x,
>>>                 */
>>>                if (bd.remainder < mbus->buswidth)
>>>                        early_bytes = bd.remainder;
>>> -             else if ((mbus->addr) % (mbus->buswidth)) {
>>> -                     early_bytes = mbus->buswidth - (mbus->addr) %
>>> -                             (mbus->buswidth);
>>> +             else if (bus_addr_offset(mbus)) {
>>> +                     early_bytes = mbus->buswidth - bus_addr_offset(mbus);
>>>                        if ((bd.remainder - early_bytes) < mbus->buswidth)
>>>                                early_bytes = bd.remainder;
>>>                }
>>> @@ -928,7 +932,7 @@ static int pl08x_fill_llis_for_desc(struct pl08x_driver_data *pl08x,
>>>                         * Master now aligned
>>>                         * - if slave is not then we must set its width down
>>>                         */
>>> -                     if (sbus->addr % sbus->buswidth) {
>>> +                     if (bus_addr_offset(sbus)) {
>>>                                dev_dbg(&pl08x->adev->dev,
>>>                                        "%s set down bus width to one byte\n",
>>>                                        __func__);
>>> --
>>> 1.7.12.1
>>>
>>
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