linux-kernel - Re: [PATCH v2 0/3] iio: adc: ad4695: add new regmap callbacks, timing improvements

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Message-ID: <1390b66e-a9dc-42ee-a692-34a98146213f@baylibre.com>
Date: Wed, 13 Nov 2024 14:58:55 -0600
From: David Lechner <dlechner@...libre.com>
To: Trevor Gamblin <tgamblin@...libre.com>,
 Lars-Peter Clausen <lars@...afoo.de>,
 Michael Hennerich <Michael.Hennerich@...log.com>,
 Nuno Sá <nuno.sa@...log.com>,
 Jonathan Cameron <jic23@...nel.org>
Cc: Jonathan Cameron <Jonathan.Cameron@...wei.com>,
 linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/3] iio: adc: ad4695: add new regmap callbacks, timing
 improvements

On 11/13/24 2:52 PM, Trevor Gamblin wrote:
> The AD4695 driver currently operates all SPI reads/writes at the speed
> appropriate for register access, rather than the max rate for the bus.
> Data reads should ideally operate at the latter speed, but making this
> change universally makes it possible for data to be corrupted during use
> and for unexpected behavior to occur on driver subsequent driver
> binds/unbinds. To solve this, introduce custom regmap bus callbacks for
> the driver that explicitly set a lower speed only for these operations.
> 
> The first patch in this series is a fix introduced after discovering the
> corresponding issue during testing of the callbacks. This is a timing
> fix that ensures the AD4695 datasheet's timing specs are met, as before
> the busy signal would sometimes fail to toggle again following the end
> of the conversion sequence. Adding an extra delay in the form of a blank
> transfer before every CS deassert in ad4695_buffer_preenable() allows
> this requirement to be met. The patch also makes similar changes in
> ad4695_read_one_sample() (while also tidying that function somewhat) to
> make sure that single reads are still functional with the regmap change.
> 
> The second patch is an improvement that increases the robustness of the
> exit message in ad4695_exit_conversion_mode(), this time by adding a
> delay before the actual exit command. This helps avoid the possibility
> that the exit message will be read as data, causing corruption on some
> buffered reads.
> 
> For additional context, see:
> https://lore.kernel.org/linux-iio/20241028163907.00007e12@Huawei.com/
> 
> Suggested-by: David Lechner <dlechner@...libre.com>
> Signed-off-by: Trevor Gamblin <tgamblin@...libre.com>
> ---
Reviewed-by: David Lechner <dlechner@...libre.com>
Tested-by: David Lechner <dlechner@...libre.com>