linux-kernel - Re: [PATCH 02/18] DMAENGINE: ste_dma40: only write phy channel config first time

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Message-ID: <AANLkTinR-mwXyrGlrCg2TCR3DtPewBPnaoZf_MWySJzX@mail.gmail.com>
Date:	Fri, 11 Jun 2010 15:23:26 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	Linus Walleij <linus.walleij@...ricsson.com>
Cc:	linux-kernel@...r.kernel.org,
	Jonas Aaberg <jonas.aberg@...ricsson.com>
Subject: Re: [PATCH 02/18] DMAENGINE: ste_dma40: only write phy channel config 
	first time

On Tue, Jun 1, 2010 at 5:20 AM, Linus Walleij
<linus.walleij@...ricsson.com> wrote:
> We only need to write the configuration to a physical channel if
> it is free, else it is already written.
>
> Signed-off-by: Jonas Aaberg <jonas.aberg@...ricsson.com>
> Signed-off-by: Linus Walleij <linus.walleij@...ricsson.com>
> ---
>  drivers/dma/ste_dma40.c |   19 +++++++++++++------
>  1 files changed, 13 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/dma/ste_dma40.c b/drivers/dma/ste_dma40.c
> index 4618d6c..1cd1ff7 100644
> --- a/drivers/dma/ste_dma40.c
> +++ b/drivers/dma/ste_dma40.c
> @@ -1211,9 +1211,9 @@ out:
>  }
>
>  static int d40_config_chan(struct d40_chan *d40c,
> -                          struct stedma40_chan_cfg *info)
> +                          struct stedma40_chan_cfg *info,
> +                          bool is_free_phy)
>  {
> -
>        /* Fill in basic CFG register values */
>        d40_phy_cfg(&d40c->dma_cfg, &d40c->src_def_cfg,
>                    &d40c->dst_def_cfg, d40c->log_num != D40_PHY_CHAN);
> @@ -1230,8 +1230,14 @@ static int d40_config_chan(struct d40_chan *d40c,
>                                d40c->dma_cfg.dst_dev_type * 32 + 16;
>        }
>
> -       /* Write channel configuration to the DMA */
> -       return d40_config_write(d40c);
> +       /*
> +        * Only write channel configuration to the DMA if the physical
> +        * resource is free. In case of multiple logical channels
> +        * on the same physical resource, only the first write is necessary.
> +        */
> +       if (is_free_phy)
> +               return d40_config_write(d40c);
> +       return 0;
>  }
>
>  static int d40_config_memcpy(struct d40_chan *d40c)
> @@ -1691,7 +1697,7 @@ static int d40_alloc_chan_resources(struct dma_chan *chan)
>        unsigned long flags;
>        struct d40_chan *d40c =
>                container_of(chan, struct d40_chan, chan);
> -
> +       bool is_free_phy;
>        spin_lock_irqsave(&d40c->lock, flags);
>
>        d40c->completed = chan->cookie = 1;
> @@ -1705,6 +1711,7 @@ static int d40_alloc_chan_resources(struct dma_chan *chan)
>                if (err)
>                        goto err_alloc;
>        }
> +       is_free_phy = (d40c->phy_chan == NULL);
>

It seems like d40_config_chan() just wants to be open coded in
d40_alloc_chan_resources().  It does not have its own local variables,
and the only thing that returns an error is d40_config_write().

While trying to figure out why this flag was needed I happened to
notice a gratuitous use of gotos in d40_allocate_channel().  Can we
make this function easier to read by just returning -EINVAL directly
when those tests fail?

--
Dan
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