linux-kernel - Re: [PATCH 1/2] dmaengine: tegra: Add terminate() for Tegra234

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Date:   Thu, 7 Jul 2022 11:40:02 +0100
From:   Jon Hunter <jonathanh@...dia.com>
To:     Akhil R <akhilrajeev@...dia.com>, dmaengine@...r.kernel.org,
        ldewangan@...dia.com, linux-kernel@...r.kernel.org,
        linux-tegra@...r.kernel.org, p.zabel@...gutronix.de,
        thierry.reding@...il.com, vkoul@...nel.org, robh+dt@...nel.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH 1/2] dmaengine: tegra: Add terminate() for Tegra234


On 07/07/2022 11:27, Akhil R wrote:
> In certain cases where the DMA client bus gets corrupted or if the
> end device ceases to send/receive data, DMA can wait indefinitely
> for the data to be received/sent. Attempting to terminate the transfer
> will put the DMA in pause flush mode and it remains there.
> 
> The channel is irrecoverable once this pause times out in Tegra194 and
> earlier chips. Whereas, from Tegra234, it can be recovered by disabling
> the channel and reprograming it.
> 
> Hence add a new terminate() function that ignores the outcome of
> dma_pause() and disables the channel.
> 
> Signed-off-by: Akhil R <akhilrajeev@...dia.com>
> ---
>   arch/arm64/boot/dts/nvidia/tegra234.dtsi |  5 +++--
>   drivers/dma/tegra186-gpc-dma.c           | 26 ++++++++++++++++++++++--
>   2 files changed, 27 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm64/boot/dts/nvidia/tegra234.dtsi b/arch/arm64/boot/dts/nvidia/tegra234.dtsi
> index cf611eff7f6b..83d1ad7d3c8c 100644
> --- a/arch/arm64/boot/dts/nvidia/tegra234.dtsi
> +++ b/arch/arm64/boot/dts/nvidia/tegra234.dtsi
> @@ -22,8 +22,9 @@
>   		ranges = <0x0 0x0 0x0 0x40000000>;
>   
>   		gpcdma: dma-controller@...0000 {
> -			compatible = "nvidia,tegra194-gpcdma",
> -				      "nvidia,tegra186-gpcdma";
> +			compatible = "nvidia,tegra234-gpcdma",
> +				     "nvidia,tegra194-gpcdma",
> +				     "nvidia,tegra186-gpcdma";
>   			reg = <0x2600000 0x210000>;
>   			resets = <&bpmp TEGRA234_RESET_GPCDMA>;
>   			reset-names = "gpcdma";

I think that this should be split into two patches.

> diff --git a/drivers/dma/tegra186-gpc-dma.c b/drivers/dma/tegra186-gpc-dma.c
> index 05cd451f541d..fa9bda4a2bc6 100644
> --- a/drivers/dma/tegra186-gpc-dma.c
> +++ b/drivers/dma/tegra186-gpc-dma.c
> @@ -157,8 +157,8 @@
>    * If any burst is in flight and DMA paused then this is the time to complete
>    * on-flight burst and update DMA status register.
>    */
> -#define TEGRA_GPCDMA_BURST_COMPLETE_TIME	20
> -#define TEGRA_GPCDMA_BURST_COMPLETION_TIMEOUT	100
> +#define TEGRA_GPCDMA_BURST_COMPLETE_TIME	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
> @@ -432,6 +432,17 @@ static int tegra_dma_device_resume(struct dma_chan *dc)
>   	return 0;
>   }
>   
> +static inline int tegra_dma_pause_noerr(struct tegra_dma_channel *tdc)
> +{
> +	/* Return 0 irrespective of PAUSE status.
> +	 * This is useful to recover channels that can exit out of flush
> +	 * state when the channel is disabled.
> +	 */
> +
> +	tegra_dma_pause(tdc);
> +	return 0;
> +}

The commit message says that "add a new terminate() function that 
ignores the outcome of dma_pause() and disables the channel". But I only 
see pause being done here.

> +
>   static void tegra_dma_disable(struct tegra_dma_channel *tdc)
>   {
>   	u32 csr, status;
> @@ -1292,6 +1303,14 @@ static const struct tegra_dma_chip_data tegra194_dma_chip_data = {
>   	.terminate = tegra_dma_pause,
>   };
>   
> +static const struct tegra_dma_chip_data tegra234_dma_chip_data = {
> +	.nr_channels = 31,
> +	.channel_reg_size = SZ_64K,
> +	.max_dma_count = SZ_1G,
> +	.hw_support_pause = true,
> +	.terminate = tegra_dma_pause_noerr,
> +};
> +
>   static const struct of_device_id tegra_dma_of_match[] = {
>   	{
>   		.compatible = "nvidia,tegra186-gpcdma",
> @@ -1299,6 +1318,9 @@ static const struct of_device_id tegra_dma_of_match[] = {
>   	}, {
>   		.compatible = "nvidia,tegra194-gpcdma",
>   		.data = &tegra194_dma_chip_data,
> +	}, {
> +		.compatible = "nvidia,tegra234-gpcdma",
> +		.data = &tegra234_dma_chip_data,
>   	}, {
>   	},
>   };

-- 
nvpublic