linux-kernel - Re: [PATCH V12 2/7] dma: hidma: Add Device Tree support

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Message-ID: <20160115151637.GJ3262@leverpostej>
Date:	Fri, 15 Jan 2016 15:16:38 +0000
From:	Mark Rutland <mark.rutland@....com>
To:	Sinan Kaya <okaya@...eaurora.org>
Cc:	dmaengine@...r.kernel.org, timur@...eaurora.org,
	devicetree@...r.kernel.org, cov@...eaurora.org,
	vinod.koul@...el.com, jcm@...hat.com, agross@...eaurora.org,
	arnd@...db.de, linux-arm-msm@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V12 2/7] dma: hidma: Add Device Tree support

On Mon, Jan 11, 2016 at 09:45:42AM -0500, Sinan Kaya wrote:
> Add documentation for the Qualcomm Technologies HIDMA driver.

s/driver/binding/


> Signed-off-by: Sinan Kaya <okaya@...eaurora.org>
> Acked-by: Rob Herring <robh@...nel.org>
> ---
>  .../devicetree/bindings/dma/qcom_hidma_mgmt.txt    | 79 ++++++++++++++++++++++
>  1 file changed, 79 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/dma/qcom_hidma_mgmt.txt
> 
> diff --git a/Documentation/devicetree/bindings/dma/qcom_hidma_mgmt.txt b/Documentation/devicetree/bindings/dma/qcom_hidma_mgmt.txt
> new file mode 100644
> index 0000000..0e6ed1f
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/dma/qcom_hidma_mgmt.txt
> @@ -0,0 +1,79 @@
> +Qualcomm Technologies HIDMA Management interface
> +
> +Qualcomm Technologies HIDMA is a high speed DMA device. It only supports
> +memcpy and memset capabilities. It has been designed for virtualized
> +environments.
> +
> +Each HIDMA HW instance consists of multiple DMA channels. These channels
> +share the same bandwidth. The bandwidth utilization can be parititioned
> +among channels based on the priority and weight assignments.
> +
> +There are only two priority levels and 15 weigh assignments possible.
> +
> +Other parameters here determine how much of the system bus this HIDMA
> +instance can use like maximum read/write request and and number of bytes to
> +read/write in a single burst.
> +
> +Main node required properties:
> +- compatible: "qcom,hidma-mgmt-1.0";
> +- reg: Address range for DMA device
> +- dma-channels: Number of channels supported by this DMA controller.
> +- max-write-burst-bytes: Maximum write burst in bytes. A memcpy requested is
> +  fragmented to multiples of this amount.
> +- max-read-burst-bytes: Maximum read burst in bytes. A memcpy request is
> +  fragmented to multiples of this amount.
> +- max-write-transactions: Maximum write transactions to perform in a burst
> +- max-read-transactions: Maximum read transactions to perform in a burst

Just to check, where do these max-* values come from?

Are they some correctness requirement of the bus this is attached to?

Are they tuning values?

The latter doesn't really belong in the DT. Given they're writeable from
the driver, it seems like that's what they are...

> +- channel-reset-timeout-cycles: Channel reset timeout in cycles for this SOC.

I'm not sure what this means. Could you elaborate on this is?

> +
> +Sub-nodes:
> +
> +HIDMA has one or more DMA channels that are used to move data from one
> +memory location to another.
> +
> +Each DMA channel is described as a sub-node under the management object.
> +When a transfer channel is given to the guest operating system, only the channel
> +object is created. The drivers have support for both flat and hierarchical
> +configuration.

Don't mention drivers here.

All you need to state is that when the OS is not in control of the
management interface (i.e. it's a guest), the channel nodes appear on
their own, not under a management node.

Other than the above questions, this looks ok to me.

Thanks,
Mark.

> +
> +Required properties:
> +- compatible: must contain "qcom,hidma-1.0"
> +- reg: Addresses for the transfer and event channel
> +- interrupts: Should contain the event interrupt
> +- desc-count: Number of asynchronous requests this channel can handle
> +- channel-index: The HW event channel completions will be delivered.
> +
> +Example:
> +
> +Hypervisor OS configuration:
> +
> +	hidma-mgmt@...84000 = {
> +		compatible = "qcom,hidma-mgmt-1.0";
> +		reg = <0xf9984000 0x15000>;
> +		dma-channels = <6>;
> +		max-write-burst-bytes = <1024>;
> +		max-read-burst-bytes = <1024>;
> +		max-write-transactions = <31>;
> +		max-read-transactions = <31>;
> +		channel-reset-timeout-cycles = <0x500>;
> +
> +		hidma_24: dma-controller@...c050000 {
> +			compatible = "qcom,hidma-1.0";
> +			reg = <0 0x5c050000 0x0 0x1000>,
> +			      <0 0x5c0b0000 0x0 0x1000>;
> +			interrupts = <0 389 0>;
> +			desc-count = <10>;
> +			channel-index = <4>;
> +		};
> +	};
> +
> +Guest OS configuration:
> +
> +	hidma_24: dma-controller@...c050000 {
> +		compatible = "qcom,hidma-1.0";
> +		reg = <0 0x5c050000 0x0 0x1000>,
> +		      <0 0x5c0b0000 0x0 0x1000>;
> +		interrupts = <0 389 0>;
> +		desc-count = <10>;
> +		channel-index = <4>;
> +	};
> -- 
> Qualcomm Technologies, Inc. on behalf of Qualcomm Innovation Center, Inc.
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project
>