linux-kernel - Re: [PATCH v2 4/5] ARM: dts: imx7: add GPMI NAND

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Message-ID: <0149534ab05adac384070fe432d83c48@agner.ch>
Date:   Thu, 25 May 2017 01:22:27 -0700
From:   Stefan Agner <stefan@...er.ch>
To:     Han Xu <han.xu@....com>
Cc:     dwmw2@...radead.org, computersforpeace@...il.com,
        boris.brezillon@...e-electrons.com, marek.vasut@...il.com,
        richard@....at, cyrille.pitchen@...el.com, robh+dt@...nel.org,
        mark.rutland@....com, shawnguo@...nel.org, kernel@...gutronix.de,
        fabio.estevam@...escale.com,
        "LW@...O-electronics.de" <LW@...o-electronics.de>,
        linux-mtd@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/5] ARM: dts: imx7: add GPMI NAND

On 2017-05-04 15:59, Han Xu wrote:
> On 05/04/2017 04:50 PM, Stefan Agner wrote:
>> On 2017-05-04 12:13, Han Xu wrote:
>>> On 04/21/2017 08:23 PM, Stefan Agner wrote:
>>>> Add i.MX 7 GPMI NAND module.
>>>>
>>>> Signed-off-by: Stefan Agner <stefan@...er.ch>
>>>> ---
>>>>    arch/arm/boot/dts/imx7s.dtsi | 31 +++++++++++++++++++++++++++++++
>>>>    1 file changed, 31 insertions(+)
>>>>
>>>> diff --git a/arch/arm/boot/dts/imx7s.dtsi b/arch/arm/boot/dts/imx7s.dtsi
>>>> index 843eb379e1ea..9645257638d4 100644
>>>> --- a/arch/arm/boot/dts/imx7s.dtsi
>>>> +++ b/arch/arm/boot/dts/imx7s.dtsi
>>>> @@ -995,5 +995,36 @@
>>>>    				status = "disabled";
>>>>    			};
>>>>    		};
>>>> +
>>>> +		dma_apbh: dma-apbh@...00000 {
>>>> +			compatible = "fsl,imx7d-dma-apbh", "fsl,imx28-dma-apbh";
>>>> +			reg = <0x33000000 0x2000>;
>>>> +			interrupts = <GIC_SPI 12 IRQ_TYPE_LEVEL_HIGH>,
>>>> +				     <GIC_SPI 12 IRQ_TYPE_LEVEL_HIGH>,
>>>> +				     <GIC_SPI 12 IRQ_TYPE_LEVEL_HIGH>,
>>>> +				     <GIC_SPI 12 IRQ_TYPE_LEVEL_HIGH>;
>>>> +			interrupt-names = "gpmi0", "gpmi1", "gpmi2", "gpmi3";
>>>> +			#dma-cells = <1>;
>>>> +			dma-channels = <4>;
>>>> +			clocks = <&clks IMX7D_NAND_USDHC_BUS_ROOT_CLK>,
>>>> +				<&clks IMX7D_NAND_ROOT_CLK>;
>>>> +			clock-names = "dma_apbh_bch", "dma_apbh_io";
>>>> +		};
>>> Do you need some patches to enable all clks for APBH DMA? Refer to
>>> https://emea01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpatchwork.ozlabs.org%2Fpatch%2F551967%2F&data=01%7C01%7Chan.xu%40nxp.com%7C98493f7e475341dbf67008d49337b441%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0&sdata=FH9k%2FC4VcVCeyidkRgUJ5Ahu4%2B%2FlDAjXVwO0DY7XMhA%3D&reserved=0
>>>
>> Oh I see, with the current code and this device tree we actually only
>> enable the first clock... But it seems to work in practice...
>>
>> What is interesting, the chapter 5.2.5 System Clocks only describes
>> APBHDMA, and no GPMI module.
>>
>> Chapter 9.4 about APBH-Bridge-DMA bridge only specifies "hclk" as clock
>> sources.
>>
>> When looking at the table in chapter 5.2.5, hclk is
>> NAND_USDHC_BUS_CLK_ROOT
>>
>> Module    Syste Module Clock   Clock Root
>> APBHDMA   apbhdma.hclk         NAND_USDHC_BUS_CLK_ROOT
>>
>> So my guess is that the actual DMA controller should work fine with
>> IMX7D_NAND_USDHC_BUS_ROOT_CLK only. It is only the GPMI module which
>> needs the NAND_ROOT_CLK. My guess is since the APBHDMA controller is
>> only used for GPMI these days, it has been combined in one module in the
>> table in chapter 5.2.5.
>>
>> So we could actually only specify:
>>
>> clocks = <&clks IMX7D_NAND_USDHC_BUS_ROOT_CLK>;
>>
>> Tested with this and NAND seems to work fine.
>>
>> Also tested accessing APBHDMA register in U-Boot with
>> IMX7D_NAND_ROOT_CLK disabled, it worked fine.
>>
>> What do you think? Should we go with this?
>>
>> This probably even saves power since GPMI's runtime clock management
>> disables IMX7D_NAND_ROOT_CLK when NAND is idle (according to the
>> nand_root_clk counter in clk_summary and the root clock register at
>> 0x3038AA00).
> 
> It also surprised me how it can work on your side, I remember we made 
> the code change for some purpose, please give me some time I can check 
> if the doc is wrong.
> 

Hi Han,

Do you have an update to this?

Otherwise, I will send out a version which only uses
IMX7D_NAND_USDHC_BUS_ROOT_CLK for now. This binding is already defined
and needs no driver change. We can still extend the binding (and
ddriver) when it turns out it is actually required.

--
Stefan

>> --
>> Stefan
>>
>>>> +
>>>> +		gpmi: gpmi-nand@...02000{
>>>> +			compatible = "fsl,imx7d-gpmi-nand";
>>>> +			#address-cells = <1>;
>>>> +			#size-cells = <1>;
>>>> +			reg = <0x33002000 0x2000>, <0x33004000 0x4000>;
>>>> +			reg-names = "gpmi-nand", "bch";
>>>> +			interrupts = <GIC_SPI 14 IRQ_TYPE_LEVEL_HIGH>;
>>>> +			interrupt-names = "bch";
>>>> +			clocks = <&clks IMX7D_NAND_ROOT_CLK>,
>>>> +				<&clks IMX7D_NAND_USDHC_BUS_ROOT_CLK>;
>>>> +			clock-names = "gpmi_io", "gpmi_bch_apb";
>>>> +			dmas = <&dma_apbh 0>;
>>>> +			dma-names = "rx-tx";
>>>> +			status = "disabled";
>>>> +		};
>>>>    	};
>>>>    };