linux-kernel - Re: [PATCH RESEND v2 3/3] dmaengine: tegra: Add support for dma-channel-mask

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Date:   Thu, 20 Oct 2022 21:16:04 -0500
From:   Rob Herring <robh@...nel.org>
To:     Akhil R <akhilrajeev@...dia.com>
Cc:     ldewangan@...dia.com, jonathanh@...dia.com, vkoul@...nel.org,
        thierry.reding@...il.com, p.zabel@...gutronix.de,
        dmaengine@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        krzysztof.kozlowski+dt@...aro.org, sfr@...b.auug.org.au
Subject: Re: [PATCH RESEND v2 3/3] dmaengine: tegra: Add support for
 dma-channel-mask

On Thu, Oct 20, 2022 at 02:03:22PM +0530, Akhil R wrote:
> Add support for dma-channel-mask so that only the specified channels
> are used. This helps to reserve some channels for the firmware.
> 
> This was initially achieved by limiting the channel number to 31 in
> the driver and adjusting the register address to skip channel0 which
> was reserved for a firmware. Now, with this change, the driver can
> align more to the actual hardware which has 32 channels.
> 
> Signed-off-by: Akhil R <akhilrajeev@...dia.com>
> Reviewed-by: Jon Hunter <jonathanh@...dia.com>
> ---
>  drivers/dma/tegra186-gpc-dma.c | 37 +++++++++++++++++++++++++++-------
>  1 file changed, 30 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/dma/tegra186-gpc-dma.c b/drivers/dma/tegra186-gpc-dma.c
> index fa9bda4a2bc6..1d1180db6d4e 100644
> --- a/drivers/dma/tegra186-gpc-dma.c
> +++ b/drivers/dma/tegra186-gpc-dma.c
> @@ -161,7 +161,10 @@
>  #define TEGRA_GPCDMA_BURST_COMPLETION_TIMEOUT	5000 /* 5 msec */
>  
>  /* Channel base address offset from GPCDMA base address */
> -#define TEGRA_GPCDMA_CHANNEL_BASE_ADD_OFFSET	0x20000
> +#define TEGRA_GPCDMA_CHANNEL_BASE_ADDR_OFFSET	0x10000
> +
> +/* Default channel mask reserving channel0 */
> +#define TEGRA_GPCDMA_DEFAULT_CHANNEL_MASK	0xfffffffe
>  
>  struct tegra_dma;
>  struct tegra_dma_channel;
> @@ -246,6 +249,7 @@ struct tegra_dma {
>  	const struct tegra_dma_chip_data *chip_data;
>  	unsigned long sid_m2d_reserved;
>  	unsigned long sid_d2m_reserved;
> +	u32 chan_mask;
>  	void __iomem *base_addr;
>  	struct device *dev;
>  	struct dma_device dma_dev;
> @@ -1288,7 +1292,7 @@ static struct dma_chan *tegra_dma_of_xlate(struct of_phandle_args *dma_spec,
>  }
>  
>  static const struct tegra_dma_chip_data tegra186_dma_chip_data = {
> -	.nr_channels = 31,
> +	.nr_channels = 32,

This is an ABI break. A new kernel with an old DTB will use 32 channels 
instead of 31. You should leave this and use the dma-channel-mask to 
enable all 32 channels.

Rob