linux-kernel - Re: [PATCH v2 2/5] mtd: nand: Qualcomm NAND controller driver

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Date:	Thu, 30 Jul 2015 12:23:45 +0530
From:	Archit Taneja <architt@...eaurora.org>
To:	Stephen Boyd <sboyd@...eaurora.org>
CC:	dehrenberg@...gle.com, linux-arm-msm@...r.kernel.org,
	cernekee@...il.com, linux-kernel@...r.kernel.org,
	linux-mtd@...ts.infradead.org, agross@...eaurora.org,
	computersforpeace@...il.com
Subject: Re: [PATCH v2 2/5] mtd: nand: Qualcomm NAND controller driver



On 7/30/2015 12:03 AM, Stephen Boyd wrote:
> On 07/29, Archit Taneja wrote:
>> On 07/29/2015 07:18 AM, Stephen Boyd wrote:
>>> On 07/27/2015 09:34 PM, Archit Taneja wrote:
>>>> Hi,
>>>>
>>>> On 07/25/2015 06:21 AM, Stephen Boyd wrote:
>>>>> On 07/21/2015 03:34 AM, Archit Taneja wrote:
>>>>>
>>>>>> +              int size)
>>>>>> +{Looks like a
>>>>>> +    struct desc_info *desc;
>>>>>> +    struct dma_async_tx_descriptor *dma_desc;
>>>>>> +    struct scatterlist *sgl;
>>>>>> +    int r;
>>>>>> +
>>>>>> +    desc = kzalloc(sizeof(*desc), GFP_KERNEL);
>>>>>> +    if (!desc)
>>>>>> +        return -ENOMEM;
>>>>>> +
>>>>>> +    list_add_tail(&desc->list, &this->list);
>>>>>> +
>>>>>> +    sgl = &desc->sgl;
>>>>>> +
>>>>>> +    sg_init_one(sgl, vaddr, size);
>>>>>> +
>>>>>> +    desc->dir = DMA_MEM_TO_DEV;
>>>>>> +
>>>>>> +    r = dma_map_sg(this->dev, sgl, 1, desc->dir);
>>>>>> +    if (r == 0)
>>>>>> +        goto err;
>>>>>
>>>>> Should we return an error in this case? Looks like return 0.
>>>>
>>>> dma_map_sg returns the number of sg entries successfully mapped. In
>>>> this case, it should be 1.
>>>
>>> Right, but this function returns 0 (success?) if we failed to map anything.
>>
>> Yes. The return value is number of entries successfully mapped.
>> dma_map_sg is a macro that is replaced by dma_map_sg_attrs. Its
>> comment
>> says:
>>
>> "dma_maps_sg_attrs returns 0 on error and > 0 on success. It should
>> never return a value < 0."
>
> Yes, and so this function that calls dma_map_sg() is going to
> return 0 to the caller when it didn't do what it was asked to do?

Ah, I get your point now :p. I thought you were referring to the
return value of dma_map_sg, and not write_data_dma. Will fix this.

Archit

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