linux-kernel - Re: [PATCH] iio: amplifiers: ada4250: use DMA-safe memory for regmap_bulk

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Message-ID: <9cdc7053-ae22-4ad5-801c-46df7398ebf9@baylibre.com>
Date: Sat, 19 Apr 2025 13:07:25 -0500
From: David Lechner <dlechner@...libre.com>
To: Andy Shevchenko <andy.shevchenko@...il.com>
Cc: Antoniu Miclaus <antoniu.miclaus@...log.com>,
 Lars-Peter Clausen <lars@...afoo.de>,
 Michael Hennerich <Michael.Hennerich@...log.com>,
 Jonathan Cameron <jic23@...nel.org>, Nuno Sá
 <nuno.sa@...log.com>, Jonathan Cameron <Jonathan.Cameron@...wei.com>,
 "linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] iio: amplifiers: ada4250: use DMA-safe memory for
 regmap_bulk_read()

On 4/19/25 10:03 AM, Andy Shevchenko wrote:
> On Fri, Apr 18, 2025 at 02:09:04PM -0500, David Lechner wrote:
>> On 4/18/25 1:58 PM, Andy Shevchenko wrote:
>>> пʼятниця, 18 квітня 2025 р. David Lechner <dlechner@...libre.com <mailto:dlechner@...libre.com>> пише:
>>>
>>>     Use DMA-safe memory instead of stack-allocated memory for the call to
>>>     regmap_bulk_read() in the ada4250_init() function as this could be used
>>>     directly by a SPI controller.
>>>
>>> Sorry, but can you elaborate more on this? If driver doesn’t override the
>>> callbacks the regmap SPI uses spi_write_then_read() which is supposed to be
>>> dma safe. 
>>
>> Ah, I didn't dig that far down. Will send a new patch that just cleans up the
>> unnecessary alignment and unaligned call.
> 
> But do you have a real life issue with that? Coincidentally we discussed
> similar case in another driver with colleague of mine, and he insists that it
> might be still broken (somewhere).
> 

Some drivers that use regmap with SPI implement their own read and write
callbacks if the default one doesn't work, so maybe something like that?