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

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Date:   Mon, 4 Jan 2021 04:08:50 +0000
From:   "Sia, Jee Heng" <jee.heng.sia@...el.com>
To:     Eugeniy Paltsev <Eugeniy.Paltsev@...opsys.com>,
        Vinod Koul <vkoul@...nel.org>
CC:     "andriy.shevchenko@...ux.intel.com" 
        <andriy.shevchenko@...ux.intel.com>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>
Subject: RE: [PATCH v8 13/16] dmaengine: dw-axi-dmac: Add Intel KeemBay AxiDMA
 handshake



> -----Original Message-----
> From: Eugeniy Paltsev <Eugeniy.Paltsev@...opsys.com>
> Sent: 31 December 2020 8:44 PM
> To: Sia, Jee Heng <jee.heng.sia@...el.com>; Vinod Koul
> <vkoul@...nel.org>
> Cc: andriy.shevchenko@...ux.intel.com; dmaengine@...r.kernel.org;
> linux-kernel@...r.kernel.org; devicetree@...r.kernel.org;
> robh+dt@...nel.org
> Subject: Re: [PATCH v8 13/16] dmaengine: dw-axi-dmac: Add Intel
> KeemBay AxiDMA handshake
> 
> Hi Sia Jee Heng,
> 
> see my comments inlined:
> 
> > From: Sia Jee Heng <jee.heng.sia@...el.com>
> > Sent: Tuesday, December 29, 2020 07:47
> > To: vkoul@...nel.org; Eugeniy Paltsev; robh+dt@...nel.org
> > Cc: andriy.shevchenko@...ux.intel.com;
> dmaengine@...r.kernel.org;
> > linux-kernel@...r.kernel.org; devicetree@...r.kernel.org
> > 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@...ux.intel.com>
> > Signed-off-by: Sia Jee Heng <jee.heng.sia@...el.com>
> > ---
> >  .../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.
[>>] OK, I can change the code in such a way that dw_axi_dma_set_hw_channel() will be executed only if apb_reg is valid.
> 
> >         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.
[>>] Sure, same method described above will be used.
> 
> 
> >         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
> >