Re: [PATCH v8 13/16] dmaengine: dw-axi-dmac: Add Intel KeemBay AxiDMA handshake

[Eugeniy Paltsev]

Hi Sia Jee Heng,

see my comments inlined:

> From: Sia Jee Heng <jee.heng.sia@xxxxxxxxx>
> Sent: Tuesday, December 29, 2020 07:47
> To: vkoul@xxxxxxxxxx; Eugeniy Paltsev; robh+dt@xxxxxxxxxx
> Cc: andriy.shevchenko@xxxxxxxxxxxxxxx; dmaengine@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; devicetree@xxxxxxxxxxxxxxx
> Subject: [PATCH v8 13/16] dmaengine: dw-axi-dmac: Add Intel KeemBay AxiDMA handshake
> 
> Add support for Intel KeemBay AxiDMA device handshake programming.
> Device handshake number passed in to the AxiDMA shall be written to
> the Intel KeemBay AxiDMA hardware handshake registers before DMA
> operations are started.
> 
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> Signed-off-by: Sia Jee Heng <jee.heng.sia@xxxxxxxxx>
> ---
>  .../dma/dw-axi-dmac/dw-axi-dmac-platform.c    | 52 +++++++++++++++++++
>  1 file changed, 52 insertions(+)
> 
> diff --git a/drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c b/drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c
> index 062d27c61983..5e77eb3d040f 100644
> --- a/drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c
> +++ b/drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c
 [snip]
> +
> +       return 0;
> +}
> +
>  /*
>   * If DW_axi_dmac sees CHx_CTL.ShadowReg_Or_LLI_Last bit of the fetched LLI
>   * as 1, it understands that the current block is the final block in the
> @@ -626,6 +668,9 @@ dw_axi_dma_chan_prep_cyclic(struct dma_chan *dchan, dma_addr_t dma_addr,
>                 llp = hw_desc->llp;
>         } while (num_periods);
> 
> +       if (dw_axi_dma_set_hw_channel(chan->chip, chan->hw_handshake_num, true))
> +               goto err_desc_get;
> +

In this implementation 'dw_axi_dma_chan_prep_cyclic' callback will fail if
we don't have APB registers which are only specific for KeemBay.
Looking for the code of 'dw_axi_dma_chan_prep_cyclic' I don't see the reason
why it shouldn't work for vanila DW AXI DMAC without this extension. So, could
you please change this so we wouldn't reject dw_axi_dma_chan_prep_cyclic in case
of APB registers are missed.

>         return vchan_tx_prep(&chan->vc, &desc->vd, flags);
> 
>  err_desc_get:
> @@ -684,6 +729,9 @@ dw_axi_dma_chan_prep_slave_sg(struct dma_chan *dchan, struct scatterlist *sgl,
>                 llp = hw_desc->llp;
>         } while (sg_len);
> 
> +       if (dw_axi_dma_set_hw_channel(chan->chip, chan->hw_handshake_num, true))
> +               goto err_desc_get;
> +

Same here.


>         return vchan_tx_prep(&chan->vc, &desc->vd, flags);
> 
>  err_desc_get:
> @@ -959,6 +1007,10 @@ static int dma_chan_terminate_all(struct dma_chan *dchan)
>                 dev_warn(dchan2dev(dchan),
>                          "%s failed to stop\n", axi_chan_name(chan));
> 
> +       if (chan->direction != DMA_MEM_TO_MEM)
> +               dw_axi_dma_set_hw_channel(chan->chip,
> +                                         chan->hw_handshake_num, false);
> +
>         spin_lock_irqsave(&chan->vc.lock, flags);
> 
>         vchan_get_all_descriptors(&chan->vc, &head);
> --
> 2.18.0
>