Re: [PATCH] i2c: at91: use dma safe buffers

[Michael Walle]

Am 2022-04-05 15:58, schrieb Codrin.Ciubotariu@xxxxxxxxxxxxx:
> On 05.04.2022 14:09, Michael Walle wrote:
> > Am 2022-04-05 12:02, schrieb Codrin.Ciubotariu@xxxxxxxxxxxxx:
> > > On 05.04.2022 12:38, Michael Walle wrote:
> > > > Am 2022-04-05 11:23, schrieb Codrin.Ciubotariu@xxxxxxxxxxxxx:
> > > > > > +       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.

It is not about errors, you need the exact same pointer you
got from i2c_get_dma_safe_msg_buf() to be passed to
i2c_put_dma_safe_msg_buf(). And because (in some cases, it
isn't really obvious) the dev->buf will be advanced a few
bytes, I cannot pass dev->buf to i2c_put_dma_safe_msg_buf().

-michael