linux-kernel - Re: [PATCH v2 3/4] dmaengine: stm32-dma: add support to trigger STM32 MDMA

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Message-ID: <d46e5eee-c8ae-545f-e69e-1dd2f2e71323@foss.st.com>
Date:   Tue, 19 Jul 2022 17:30:49 +0200
From:   Amelie Delaunay <amelie.delaunay@...s.st.com>
To:     Marek Vasut <marex@...x.de>, Jonathan Corbet <corbet@....net>,
        Vinod Koul <vkoul@...nel.org>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>
CC:     <linux-doc@...r.kernel.org>, <dmaengine@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 3/4] dmaengine: stm32-dma: add support to trigger STM32
 MDMA

Hi Marek,

Thanks for reviewing.

On 7/14/22 21:02, Marek Vasut wrote:
> On 7/13/22 16:21, Amelie Delaunay wrote:
> 
> [...]
> 
>> diff --git a/drivers/dma/stm32-dma.c b/drivers/dma/stm32-dma.c
>> index adb25a11c70f..3916295fe154 100644
>> --- a/drivers/dma/stm32-dma.c
>> +++ b/drivers/dma/stm32-dma.c
>> @@ -142,6 +142,8 @@
>>   #define STM32_DMA_DIRECT_MODE_GET(n)    (((n) & 
>> STM32_DMA_DIRECT_MODE_MASK) >> 2)
>>   #define STM32_DMA_ALT_ACK_MODE_MASK    BIT(4)
>>   #define STM32_DMA_ALT_ACK_MODE_GET(n)    (((n) & 
>> STM32_DMA_ALT_ACK_MODE_MASK) >> 4)
>> +#define STM32_DMA_MDMA_STREAM_ID_MASK    GENMASK(19, 16)
>> +#define STM32_DMA_MDMA_STREAM_ID_GET(n) (((n) & 
>> STM32_DMA_MDMA_STREAM_ID_MASK) >> 16)
> 
> Try FIELD_GET() from include/linux/bitfield.h
> 
> [...]
> 

Yes, but not only on this new line. I'll add a prior patch to the 
patchset to use FIELD_{GET,PREP}() helpers every where custom macros are 
used.

>> @@ -1630,6 +1670,20 @@ static int stm32_dma_probe(struct 
>> platform_device *pdev)
>>           chan->id = i;
>>           chan->vchan.desc_free = stm32_dma_desc_free;
>>           vchan_init(&chan->vchan, dd);
>> +
>> +        chan->mdma_config.ifcr = res->start;
>> +        chan->mdma_config.ifcr += (chan->id & 4) ? STM32_DMA_HIFCR : 
>> STM32_DMA_LIFCR;
>> +
>> +        chan->mdma_config.tcf = STM32_DMA_TCI;
>> +        /*
>> +         * bit0 of chan->id represents the need to left shift by 6
>> +         * bit1 of chan->id represents the need to extra left shift 
>> by 16
>> +         * TCIF0, chan->id = b0000; TCIF4, chan->id = b0100: left 
>> shift by 0*6 + 0*16
>> +         * TCIF1, chan->id = b0001; TCIF5, chan->id = b0101: left 
>> shift by 1*6 + 0*16
>> +         * TCIF2, chan->id = b0010; TCIF6, chan->id = b0110: left 
>> shift by 0*6 + 1*16
>> +         * TCIF3, chan->id = b0011; TCIF7, chan->id = b0111: left 
>> shift by 1*6 + 1*16
>> +         */
>> +        chan->mdma_config.tcf <<= (6 * (chan->id & 0x1) + 16 * 
>> ((chan->id & 0x2) >> 1));
> 
> Some sort of symbolic macros instead of open-coded constants could help 
> readability here.
> 

I agree. As the same kind of computation is done in 
stm32_dma_irq_status() and stm32_dma_irq_clear(), I'll add another prior 
patch to the patchset to introduce new macro helpers to get ISR/IFCR 
offset depending on channel id, and to get channel flags mask depending 
on channel id.

> [...]

Regards,
Amelie