Re: [PATCH V8 3/5] i2c: tegra: Add DMA Support

Dmitry Osipenko
2019-01-31T15:24:26Z

31.01.2019 18:12, Dmitry Osipenko пишет:
> 31.01.2019 9:16, Sowjanya Komatineni пишет:
>> This patch adds DMA support for Tegra I2C.
>>
>> Tegra I2C TX and RX FIFO depth is 8 words. PIO mode is used for
>> transfer size of the max FIFO depth and DMA mode is used for
>> transfer size higher than max FIFO depth to save CPU overhead.
>>
>> PIO mode needs full intervention of CPU to fill or empty FIFO's
>> and also need to service multiple data requests interrupt for the
>> same transaction. This adds delay between data bytes of the same
>> transfer when CPU is fully loaded and some slave devices has
>> internal timeout for no bus activity and stops transaction to
>> avoid bus hang. DMA mode is helpful in such cases.
>>
>> DMA mode is also helpful for Large transfers during downloading or
>> uploading FW over I2C to some external devices.
>>
>> Signed-off-by: Sowjanya Komatineni <skomatineni@nvidia.com>
>> ---
>> [V8] : Moved back dma init to i2c probe, removed ALL_PACKETS_XFER_COMPLETE
>> interrupt and using PACKETS_XFER_COMPLETE interrupt only and some
>> other fixes
>> Updated Kconfig for APB_DMA dependency
>> [V7] : Same as V6
>> [V6] : Updated for proper buffer allocation/freeing, channel release.
>> Updated to use exact xfer size for syncing dma buffer.
>> [V5] : Same as V4
>> [V4] : Updated to allocate DMA buffer only when DMA mode.
>> Updated to fall back to PIO mode when DMA channel request or
>> buffer allocation fails.
>> [V3] : Updated without additional buffer allocation.
>> [V2] : Updated based on V1 review feedback along with code cleanup for
>> proper implementation of DMA.
>>
>> drivers/i2c/busses/Kconfig | 2 +-
>> drivers/i2c/busses/i2c-tegra.c | 362 ++++++++++++++++++++++++++++++++++++++---
>> 2 files changed, 339 insertions(+), 25 deletions(-)
>
> Tegra20 crashes because of this patch:
>
[snip]
> <4>[ 3.395915] ------------[ cut here ]------------
> <2>[ 3.395919] kernel BUG at drivers/i2c/busses/i2c-tegra.c:810!
The BUG line is from:

if (status & I2C_INT_PACKET_XFER_COMPLETE) {
if (i2c_dev->is_curr_dma_xfer)
i2c_dev->msg_buf_remaining = 0;
BUG_ON(i2c_dev->msg_buf_remaining);
complete(&i2c_dev->msg_complete);
}