linux-kernel - Re: [PATCH v2] dmaengine: tegra-apb: proper default init of channel slave

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Date:	Fri, 22 Apr 2016 14:43:24 +0100
From:	Jon Hunter <jonathanh@...dia.com>
To:	Shardar Shariff Md <smohammed@...dia.com>, <ldewangan@...dia.com>,
	<vinod.koul@...el.com>, <dan.j.williams@...el.com>,
	<swarren@...dotorg.org>, <thierry.reding@...il.com>,
	<gnurou@...il.com>, <dmaengine@...r.kernel.org>,
	<linux-tegra@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] dmaengine: tegra-apb: proper default init of channel
 slave_id


On 22/04/16 13:44, Shardar Shariff Md wrote:
> Initialize default channel slave_id(req_sel) to invalid id
> (i.e max supported slave id + 1) to avoid overwriting of slave_id
> during tegra_dma_slave_config() with client data if slave_id
> is not initialized through DT
> 
> Signed-off-by: Shardar Shariff Md <smohammed@...dia.com>
> 
> ---
> - Instead of initializing the slave id to -1 define macros for
>   max slave id and invalid slave id and do the checks accordingly.
> ---
>  drivers/dma/tegra20-apb-dma.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/dma/tegra20-apb-dma.c b/drivers/dma/tegra20-apb-dma.c
> index 3871f29..2957e26 100644
> --- a/drivers/dma/tegra20-apb-dma.c
> +++ b/drivers/dma/tegra20-apb-dma.c
> @@ -114,6 +114,9 @@
>  /* Channel base address offset from APBDMA base address */
>  #define TEGRA_APBDMA_CHANNEL_BASE_ADD_OFFSET	0x1000
>  
> +#define TEGRA_APBDMA_SLAVE_ID_MAX		31
> +#define TEGRA_APBDMA_SLAVE_ID_INVALID		(TEGRA_APBDMA_SLAVE_ID_MAX + 1)
> +
>  struct tegra_dma;
>  
>  /*
> @@ -353,7 +356,7 @@ static int tegra_dma_slave_config(struct dma_chan *dc,
>  	}
>  
>  	memcpy(&tdc->dma_sconfig, sconfig, sizeof(*sconfig));
> -	if (!tdc->slave_id)
> +	if (tdc->slave_id == TEGRA_APBDMA_SLAVE_ID_INVALID)
>  		tdc->slave_id = sconfig->slave_id;
>  	tdc->config_init = true;
>  	return 0;
> @@ -1236,7 +1239,7 @@ static void tegra_dma_free_chan_resources(struct dma_chan *dc)
>  	}
>  	pm_runtime_put(tdma->dev);
>  
> -	tdc->slave_id = 0;
> +	tdc->slave_id = TEGRA_APBDMA_SLAVE_ID_INVALID;
>  }
>  
>  static struct dma_chan *tegra_dma_of_xlate(struct of_phandle_args *dma_spec,
> @@ -1253,6 +1256,11 @@ static struct dma_chan *tegra_dma_of_xlate(struct of_phandle_args *dma_spec,
>  	tdc = to_tegra_dma_chan(chan);
>  	tdc->slave_id = dma_spec->args[0];
>  
> +	if (tdc->slave_id > TEGRA_APBDMA_SLAVE_ID_MAX) {
> +		dev_err(tdc2dev(tdc), "Invalid slave id\n");
> +		return NULL;
> +	}

Please move this test to before the dma_get_any_slave_channel(),
otherwise we could leak the DMA channel!

Cheers
Jon