linux-kernel - Re: [PATCH v4 02/10] dmaengine: Actions: Add support for S700 DMA engine

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Message-ID: <75d154d0-2962-99e6-a7c7-bf0928ec8b2a@arm.com>
Date:   Wed, 24 Jun 2020 10:35:07 +0100
From:   André Przywara <andre.przywara@....com>
To:     Vinod Koul <vkoul@...nel.org>,
        Amit Singh Tomar <amittomer25@...il.com>
Cc:     afaerber@...e.de, manivannan.sadhasivam@...aro.org,
        dan.j.williams@...el.com, cristian.ciocaltea@...il.com,
        dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-actions@...ts.infradead.org
Subject: Re: [PATCH v4 02/10] dmaengine: Actions: Add support for S700 DMA
 engine

On 24/06/2020 07:15, Vinod Koul wrote:

Hi,

> On 09-06-20, 15:47, Amit Singh Tomar wrote:
> 
>> @@ -372,6 +383,7 @@ static inline int owl_dma_cfg_lli(struct owl_dma_vchan *vchan,
>>  				  struct dma_slave_config *sconfig,
>>  				  bool is_cyclic)
>>  {
>> +	struct owl_dma *od = to_owl_dma(vchan->vc.chan.device);
>>  	u32 mode, ctrlb;
>>  
>>  	mode = OWL_DMA_MODE_PW(0);
>> @@ -427,14 +439,26 @@ static inline int owl_dma_cfg_lli(struct owl_dma_vchan *vchan,
>>  	lli->hw[OWL_DMADESC_DADDR] = dst;
>>  	lli->hw[OWL_DMADESC_SRC_STRIDE] = 0;
>>  	lli->hw[OWL_DMADESC_DST_STRIDE] = 0;
>> -	/*
>> -	 * Word starts from offset 0xC is shared between frame length
>> -	 * (max frame length is 1MB) and frame count, where first 20
>> -	 * bits are for frame length and rest of 12 bits are for frame
>> -	 * count.
>> -	 */
>> -	lli->hw[OWL_DMADESC_FLEN] = len | FCNT_VAL << 20;
>> -	lli->hw[OWL_DMADESC_CTRLB] = ctrlb;
>> +
>> +	if (od->devid == S700_DMA) {
>> +		/* Max frame length is 1MB */
>> +		lli->hw[OWL_DMADESC_FLEN] = len;
>> +		/*
>> +		 * On S700, word starts from offset 0x1C is shared between
>> +		 * frame count and ctrlb, where first 12 bits are for frame
>> +		 * count and rest of 20 bits are for ctrlb.
>> +		 */
>> +		lli->hw[OWL_DMADESC_CTRLB] = FCNT_VAL | ctrlb;
>> +	} else {
>> +		/*
>> +		 * On S900, word starts from offset 0xC is shared between
>> +		 * frame length (max frame length is 1MB) and frame count,
>> +		 * where first 20 bits are for frame length and rest of
>> +		 * 12 bits are for frame count.
>> +		 */
>> +		lli->hw[OWL_DMADESC_FLEN] = len | FCNT_VAL << 20;
>> +		lli->hw[OWL_DMADESC_CTRLB] = ctrlb;
> 
> Unfortunately this wont scale, we will keep adding new conditions for
> newer SoC's! So rather than this why not encode max frame length in
> driver_data rather than S900_DMA/S700_DMA.. In future one can add values
> for newer SoC and not code above logic again.

What newer SoCs? I don't think we should try to guess the future here.
We can always introduce further abstractions later, once we actually
*know* what we are looking at.

Besides, I don't understand what you are after. The max frame length is
1MB in both cases, it's just a matter of where to put FCNT_VAL, either
in FLEN or in CTRLB. And having an extra flag for that in driver data
sounds a bit over the top at the moment.

Cheers,
Andre.

> 
>> +static const struct of_device_id owl_dma_match[] = {
>> +	{ .compatible = "actions,s900-dma", .data = (void *)S900_DMA,},
>> +	{ .compatible = "actions,s700-dma", .data = (void *)S700_DMA,},
> 
> Is the .compatible documented, Documentation patch should come before
> the driver use patch in a series
> 
>>  static int owl_dma_probe(struct platform_device *pdev)
>>  {
>>  	struct device_node *np = pdev->dev.of_node;
>>  	struct owl_dma *od;
>>  	int ret, i, nr_channels, nr_requests;
>> +	const struct of_device_id *of_id =
>> +				of_match_device(owl_dma_match, &pdev->dev);
> 
> You care about driver_data rather than of_id, so using
> of_device_get_match_data() would be better..
> 
>>  	od = devm_kzalloc(&pdev->dev, sizeof(*od), GFP_KERNEL);
>>  	if (!od)
>> @@ -1083,6 +1116,8 @@ static int owl_dma_probe(struct platform_device *pdev)
>>  	dev_info(&pdev->dev, "dma-channels %d, dma-requests %d\n",
>>  		 nr_channels, nr_requests);
>>  
>> +	od->devid = (enum owl_dma_id)(uintptr_t)of_id->data;
> 
> Funny casts, I dont think you need uintptr_t!
>