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Date:   Sun, 7 Oct 2018 20:27:22 +0530
From:   Vinod <vkoul@kernel.org>
To:     Pierre-Yves MORDRET <pierre-yves.mordret@st.com>
Cc:     Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexandre Torgue <alexandre.torgue@st.com>,
        Maxime Coquelin <mcoquelin.stm32@gmail.com>,
        Dan Williams <dan.j.williams@intel.com>,
        devicetree@vger.kernel.org, dmaengine@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 1/7] dt-bindings: stm32-dma: Add DMA/MDMA chaining
 support bindings
Message-ID: <20181007145722.GY2372@vkoul-mobl>
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On 28-09-18, 15:01, Pierre-Yves MORDRET wrote:
> From: M'boumba Cedric Madianga <cedric.madianga@gmail.com>
> 
> This patch adds dma bindings to support DMA/MDMA chaining transfer.
> 1 bit is to manage both DMA FIFO Threshold
> 1 bit is to manage DMA/MDMA Chaining features.
> 2 bits are used to specify SDRAM size to use for DMA/MDMA chaining.

Please do mention which specific bits?

> The size in bytes of a certain order is given by the formula:
>     (2 ^ order) * PAGE_SIZE.
> The order is given by those 2 bits.
> For cyclic, whether chaining is chosen, any value above 1 can be set :
> SRAM buffer size will rely on period size and not on this DT value.
> 
> Signed-off-by: Pierre-Yves MORDRET <pierre-yves.mordret@st.com>
> ---
>   Version history:
>     v3:
>     v2:
>        * rework content
>     v1:
>        * Initial
> ---
> ---
>  .../devicetree/bindings/dma/stm32-dma.txt          | 27 +++++++++++++++++++++-
>  1 file changed, 26 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/devicetree/bindings/dma/stm32-dma.txt b/Documentation/devicetree/bindings/dma/stm32-dma.txt
> index c5f5190..2bac8c7 100644
> --- a/Documentation/devicetree/bindings/dma/stm32-dma.txt
> +++ b/Documentation/devicetree/bindings/dma/stm32-dma.txt
> @@ -17,6 +17,12 @@ Optional properties:
>  - resets: Reference to a reset controller asserting the DMA controller
>  - st,mem2mem: boolean; if defined, it indicates that the controller supports
>    memory-to-memory transfer
> +- dmas: A list of eight dma specifiers, one for each entry in dma-names.
> +  Refer to stm32-mdma.txt for more details.
> +- dma-names: should contain "ch0", "ch1", "ch2", "ch3", "ch4", "ch5", "ch6" and
> +  "ch7" and represents each STM32 DMA channel connected to a STM32 MDMA one.
> +- memory-region : phandle to a node describing memory to be used for
> +  M2M intermediate transfer between DMA and MDMA.
>  
>  Example:
>  
> @@ -36,6 +42,16 @@ Example:
>  		st,mem2mem;
>  		resets = <&rcc 150>;
>  		dma-requests = <8>;
> +		dmas = <&mdma1 8 0x10 0x1200000a 0x40026408 0x00000020 1>,
> +		       <&mdma1 9 0x10 0x1200000a 0x40026408 0x00000800 1>,
> +		       <&mdma1 10 0x10 0x1200000a 0x40026408 0x00200000 1>,
> +		       <&mdma1 11 0x10 0x1200000a 0x40026408 0x08000000 1>,
> +		       <&mdma1 12 0x10 0x1200000a 0x4002640C 0x00000020 1>,
> +		       <&mdma1 13 0x10 0x1200000a 0x4002640C 0x00000800 1>,
> +		       <&mdma1 14 0x10 0x1200000a 0x4002640C 0x00200000 1>,
> +		       <&mdma1 15 0x10 0x1200000a 0x4002640C 0x08000000 1>;
> +		dma-names = "ch0", "ch1", "ch2", "ch3", "ch4", "ch5", "ch6", "ch7";
> +		memory-region = <&sram_dmapool>;
>  	};
>  
>  * DMA client
> @@ -68,7 +84,16 @@ channel: a phandle to the DMA controller plus the following four integer cells:
>  	0x1: 1/2 full FIFO
>  	0x2: 3/4 full FIFO
>  	0x3: full FIFO
> -
> + -bit 2: Intermediate M2M transfer from/to DDR to/from SRAM throughout MDMA
> +	0: MDMA not used to generate an intermediate M2M transfer
> +	1: MDMA used to generate an intermediate M2M transfer.
> + -bit 3-4: indicated SRAM Buffer size in (2^order)*PAGE_SIZE.
> +	PAGE_SIZE is given by Linux at 4KiB: include/asm-generic/page.h.
> +	Order is given by those 2 bits starting at 0.
> +	Valid only whether Intermediate M2M transfer is set.

why do we need this as a property?

> +	For cyclic, whether Intermediate M2M transfer is chosen, any value can
> +	be set: SRAM buffer size will rely on period size and not on this DT
> +	value.
>  
>  Example:
>  
> -- 
> 2.7.4

-- 
~Vinod