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    SubjectRe: [PATCH] i2c: at91: use dma safe buffers
    Date
    On 05.04.2022 14:09, Michael Walle wrote:
    > Am 2022-04-05 12:02, schrieb Codrin.Ciubotariu@microchip.com:
    >> On 05.04.2022 12:38, Michael Walle wrote:
    >>> Am 2022-04-05 11:23, schrieb Codrin.Ciubotariu@microchip.com:
    >>>>> +       if (dev->use_dma) {
    >>>>> +               dma_buf = i2c_get_dma_safe_msg_buf(m_start, 1);
    >>>>
    >>>> If you want, you could just dev->buf = i2c_get_dma_safe...
    >>>
    >>> But where is the error handling in that case? dev->buf will
    >>> be NULL, which is eventually passed to dma_map_single().
    >>>
    >>> Also, I need the dma_buf for the i2c_put_dma_safe_msg_buf()
    >>> call anyway, because dev->buf will be modified during
    >>> processing.
    >>
    >> You still:
    >>       if (!dev->buf) {
    >>               ret = -ENOMEM;
    >>               goto out;
    >>       }
    >>
    >> So, at91_do_twi_transfer()/dma_map_single() will not be called.
    >
    > Ahh, I misunderstood you. Yes, but as I said, I need the dma_buf
    > temporary variable anyway, because dev->buf is modified, eg. see
    > at91_twi_read_data_dma_callback().
    at91_twi_read_data_dma_callback() is called as callback if
    dma_async_issue_pending(dma->chan_rx) is called.
    dma_async_issue_pending(dma->chan_rx) is called on
    at91_twi_read_data_dma(), which is called in at91_do_twi_transfer(),
    which we decided above to skip in case of error.
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