linux-kernel - Re: [PATCH] staging: fieldbus: anybuss: force address space conversion

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Date:   Tue, 21 May 2019 12:53:45 -0400
From:   Sven Van Asbroeck <thesven73@...il.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     devel@...verdev.osuosl.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Dan Carpenter <dan.carpenter@...cle.com>
Subject: Re: [PATCH] staging: fieldbus: anybuss: force address space conversion

On Tue, May 21, 2019 at 12:24 PM Greg KH <gregkh@...uxfoundation.org> wrote:
>
> what is so odd about this code that makes you have to jump through
> strange hoops that no other driver has to?
>

Basically because it creates a regmap which accesses __iomem memory,
instead of i2c/spi.

This was done because future hardware in the company's pipeline will access
device register space through spi, instead of through a parallel memory bus.

The lower driver just has to create the appropriate regmap, __iomem or
spi, and pass it to the
upper driver, which does not have to know about the exact way the h/w
gets accessed.
So regmap is used as a hw abstraction layer.

The issue here is that a regmap context is a 'void *' yet the parallel
memory base pointer
is 'void __iomem *'. And so the two are incompatible.