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Subject: Re: [PATCH v8 13/22] counter: Internalize sysfs interface code
To:     William Breathitt Gray <vilhelm.gray@gmail.com>, jic23@kernel.org
Cc:     kernel@pengutronix.de, linux-stm32@st-md-mailman.stormreply.com,
        a.fatoum@pengutronix.de, kamel.bouhara@bootlin.com,
        gwendal@chromium.org, alexandre.belloni@bootlin.com,
        linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, syednwaris@gmail.com,
        patrick.havelange@essensium.com, fabrice.gasnier@st.com,
        mcoquelin.stm32@gmail.com, alexandre.torgue@st.com,
        o.rempel@pengutronix.de, Dan Carpenter <dan.carpenter@oracle.com>
References: <cover.1613131238.git.vilhelm.gray@gmail.com>
 <3fc2580af0efd6312a64a0e107bd6fa758f0d466.1613131238.git.vilhelm.gray@gmail.com>
From:   David Lechner <david@lechnology.com>
Message-ID: <2d9c7cfe-1f26-22b4-281f-63a7a1801452@lechnology.com>
Date:   Sat, 20 Feb 2021 11:50:53 -0600
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On 2/12/21 6:13 AM, William Breathitt Gray wrote:
> This is a reimplementation of the Generic Counter driver interface.
> There are no modifications to the Counter subsystem userspace interface,
> so existing userspace applications should continue to run seamlessly.
> 
> The purpose of this patch is to internalize the sysfs interface code
> among the various counter drivers into a shared module. Counter drivers
> pass and take data natively (i.e. u8, u64, etc.) and the shared counter
> module handles the translation between the sysfs interface and the
> device drivers. This guarantees a standard userspace interface for all
> counter drivers, and helps generalize the Generic Counter driver ABI in
> order to support the Generic Counter chrdev interface (introduced in a
> subsequent patch) without significant changes to the existing counter
> drivers.
> 
> Note, Counter device registration is the same as before: drivers
> populate a struct counter_device with components and callbacks, then
> pass the structure to the devm_counter_register function. However,
> what's different now is how the Counter subsystem code handles this
> registration internally.
> 
> Whereas before callbacks would interact directly with sysfs data, this
> interaction is now abstracted and instead callbacks interact with native
> C data types. The counter_comp structure forms the basis for Counter
> extensions.
> 
> The counter-sysfs.c file contains the code to parse through the
> counter_device structure and register the requested components and
> extensions. Attributes are created and populated based on type, with
> respective translation functions to handle the mapping between sysfs and
> the counter driver callbacks.
> 
> The translation performed for each attribute is straightforward: the
> attribute type and data is parsed from the counter_attribute structure,
> the respective counter driver read/write callback is called, and sysfs
> I/O is handled before or after the driver read/write function is called.
> 
> Cc: Syed Nayyar Waris <syednwaris@gmail.com>
> Cc: Patrick Havelange <patrick.havelange@essensium.com>
> Cc: Kamel Bouhara <kamel.bouhara@bootlin.com>
> Cc: Fabrice Gasnier <fabrice.gasnier@st.com>
> Cc: Maxime Coquelin <mcoquelin.stm32@gmail.com>
> Cc: Alexandre Torgue <alexandre.torgue@st.com>
> Cc: David Lechner <david@lechnology.com>
> Cc: Dan Carpenter <dan.carpenter@oracle.com>
> Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com>
> ---

For TI eQEP bits...

Reviewed-by: David Lechner <david@lechnology.com>
Tested-by: David Lechner <david@lechnology.com>