linux-kernel - Re: [PATCH v7 2/5] media: platform: visconti: Add Toshiba Visconti Video Input Interface driver

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Message-ID: <e91dde98-b1ec-6e68-b823-9b5232a4774d@arm.com>
Date:   Mon, 21 Aug 2023 14:35:55 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        yuji2.ishikawa@...hiba.co.jp
Cc:     krzysztof.kozlowski@...aro.org, hverkuil@...all.nl,
        sakari.ailus@....fi, mchehab@...nel.org, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
        nobuhiro1.iwamatsu@...hiba.co.jp, broonie@...nel.org,
        linux-media@...r.kernel.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: [PATCH v7 2/5] media: platform: visconti: Add Toshiba Visconti
 Video Input Interface driver

On 2023-08-21 14:19, Laurent Pinchart wrote:
[...]
>>>> +	viif_dev->tables =
>>>> +		dma_alloc_wc(dev, sizeof(struct viif_table_area), &tables_dma, GFP_KERNEL);
>>>> +	if (!viif_dev->tables) {
>>>> +		dev_err(dev, "dma_alloc_wc failed\n");
>>>
>>> Are you sure DMA memory allocation errors shall be printed?
>>
>> Printing this error is useless for users in general?
>> If so, I'll drop this debug output.
> 
> Failures to allocate memory in the kernel generally result in warning
> messages being printed by the allocation function, so there's no need to
> do so manually in drivers. This being said, I check dma_alloc_wc()
> (which is a wrapper around dma_alloc_attrs()), and unless I'm missing
> something, it can return NULL without printing any error. I don't know
> if this is an oversight in some code paths taken by dma_alloc_attrs() or
> if it's on purpose. Maybe Christoph, Marek or Roben will known.

Yeah, there might be a few edge cases, but in most cases 
dma_alloc_attrs() will end up falling back to the page allocator as a 
last resort if all the more preferred allocation options fail, and thus 
complete failure should eventually cause that to scream unless 
DMA_ATTR_NO_WARN was specified.

Thanks,
Robin.