Re: [PATCH RESEND v4 1/6] dmaengine: dw: Add peripheral bus width verification

Ferry Toth
2024-09-15T21:06:09Z

Hi,

Op 14-09-2024 om 21:22 schreef Serge Semin:
> On Sat, Sep 14, 2024 at 10:12:35PM +0300, Andy Shevchenko wrote:
>> On Fri, Aug 02, 2024 at 10:50:46AM +0300, Serge Semin wrote:
>>> Currently the src_addr_width and dst_addr_width fields of the
>>> dma_slave_config structure are mapped to the CTLx.SRC_TR_WIDTH and
>>> CTLx.DST_TR_WIDTH fields of the peripheral bus side in order to have the
>>> properly aligned data passed to the target device. It's done just by
>>> converting the passed peripheral bus width to the encoded value using the
>>> __ffs() function. This implementation has several problematic sides:
>>>
>>> 1. __ffs() is undefined if no bit exist in the passed value. Thus if the
>>> specified addr-width is DMA_SLAVE_BUSWIDTH_UNDEFINED, __ffs() may return
>>> unexpected value depending on the platform-specific implementation.
>>>
>>> 2. DW AHB DMA-engine permits having the power-of-2 transfer width limited
>>> by the DMAH_Mk_HDATA_WIDTH IP-core synthesize parameter. Specifying
>>> bus-width out of that constraints scope will definitely cause unexpected
>>> result since the destination reg will be only partly touched than the
>>> client driver implied.
>>>
>>> Let's fix all of that by adding the peripheral bus width verification
>>> method and calling it in dwc_config() which is supposed to be executed
>>> before preparing any transfer. The new method will make sure that the
>>> passed source or destination address width is valid and if undefined then
>>> the driver will just fallback to the 1-byte width transfer.
>> This patch broke Intel Merrifield iDMA32 + SPI PXA2xx configuration to
>> me. Since it's first in the series and most likely the rest is
>> dependent and we are almost at the release date I propose to roll back
>> and start again after v6.12-rc1 will be out. Vinod, can we revert the
>> entire series, please?
Indeed all six need to be reverted due to dependency.
>> I guess it's not the best option, since the patch has already been
>> backported to the stable kernels anyway. Rolling back it from all of
>> them seems tiresome. Let's at least try to fix the just discovered
>> problem?
>>
>> Could you please provide more details about what exactly happening?

I can reproduce (after working around another issue with the following
tip from Andy: The DMA module is loaded _after_ the SPI, and for some
reason the DMA engine APIs haven't returned deferred probe and hence the
SPI considered the absence of DMA even if we have ACPI description
non-fatal. So, you may try to manually unload SPI and load again and it
should start showing DMA).

On 6.11.0-rc6 I get:
root@edison:~# ./spidev_test -D /dev/spidev5.1 -l
spi mode: 0x20
bits per word: 8
max speed: 500000 Hz (500 kHz)
can't send spi message: Device or resource busy
Aborted (core dumped)

And on 6.11.0-rc7 with the 6 patches reverted:

root@edison:~# ./spidev_test -D /dev/spidev5.1 -l -v
spi mode: 0x20
bits per word: 8
max speed: 500000 Hz (500 kHz)
TX | FF FF FF FF FF FF 40 00 00 00 00 95 FF FF FF FF FF FF FF FF FF FF
FF FF FF FF FF FF FF FF F0 0D  |......@.........................|
RX | FF FF FF FF FF FF 40 00 00 00 00 95 FF FF FF FF FF FF FF FF FF FF
FF FF FF FF FF FF FF FF F0 0D  |......@.........................|
>> -Serge(y)
>>
>> --
>> With Best Regards,
>> Andy Shevchenko
>>
>>