linux-kernel - Re: [PATCH 06/14] dmaengine: dma-jz4780: Add support for the JZ4725B SoC

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Message-Id: <1531350835.2021.1@smtp.crapouillou.net>
Date:   Thu, 12 Jul 2018 01:13:55 +0200
From:   Paul Cercueil <paul@...pouillou.net>
To:     Vinod <vkoul@...nel.org>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Paul Burton <paul.burton@...s.com>,
        James Hogan <jhogan@...nel.org>,
        Zubair Lutfullah Kakakhel <Zubair.Kakakhel@...tec.com>,
        Mathieu Malaterre <malat@...ian.org>,
        Daniel Silsby <dansilsby@...il.com>, dmaengine@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mips@...ux-mips.org
Subject: Re: [PATCH 06/14] dmaengine: dma-jz4780: Add support for the JZ4725B
 SoC



Le mer. 11 juil. 2018 à 14:18, Vinod <vkoul@...nel.org> a écrit :
> On 10-07-18, 17:45, Paul Cercueil wrote:
>> 
>> 
>>  Le lun. 9 juil. 2018 à 19:14, Vinod <vkoul@...nel.org> a écrit :
>>  > On 03-07-18, 14:32, Paul Cercueil wrote:
>>  > >  The JZ4725B has one DMA core starring six DMA channels.
>>  > >  As for the JZ4770, each DMA channel's clock can be enabled with
>>  > >  a register write, the difference here being that once started, 
>> it
>>  > >  is not possible to turn it off.
>>  >
>>  > ok so disable for this, right..
>>  >
>>  > >  @@ -204,6 +205,8 @@ static inline void
>>  > > jz4780_dma_chan_enable(struct jz4780_dma_dev *jzdma,
>>  > >   {
>>  > >   	if (jzdma->version == ID_JZ4770)
>>  > >   		jz4780_dma_ctrl_writel(jzdma, JZ_DMA_REG_DCKES, BIT(chn));
>>  > >  +	else if (jzdma->version == ID_JZ4725B)
>>  > >  +		jz4780_dma_ctrl_writel(jzdma, JZ_DMA_REG_DCKE, BIT(chn));
>>  >
>>  > but you are writing to a different register here..
>> 
>>  Yes. SoCs >= JZ4770 have the DCKE read-only register, and 
>> DCKES/DCKEC to
>>  set/clear bits in DCKE.
>>  On JZ4725B, DCKE is read/write, but the zeros written are ignored 
>> (at least
>>  that's what the
>>  documentation says).
> 
> and that was not documented in the log... so i though it maybe a typo.

Right, I will add a comment in-code to explain that it's normal.

> --
> ~Vinod

Thanks,
-Paul