linux-kernel - Re: [PATCH 01/10] regmap-irq: Add get_irq_reg to support unusual register layouts

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Date:   Mon, 6 Jun 2022 10:43:20 -0700
From:   Guru Das Srinagesh <quic_gurus@...cinc.com>
To:     Aidan MacDonald <aidanmacdonald.0x0@...il.com>
CC:     <linus.walleij@...aro.org>, <brgl@...ev.pl>, <robh+dt@...nel.org>,
        <krzysztof.kozlowski+dt@...aro.org>, <wens@...e.org>,
        <jic23@...nel.org>, <lee.jones@...aro.org>, <sre@...nel.org>,
        <broonie@...nel.org>, <gregkh@...uxfoundation.org>,
        <lgirdwood@...il.com>, <lars@...afoo.de>, <rafael@...nel.org>,
        <linux-gpio@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-iio@...r.kernel.org>, <linux-pm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 01/10] regmap-irq: Add get_irq_reg to support unusual
 register layouts

On Fri, Jun 03, 2022 at 02:57:05PM +0100, Aidan MacDonald wrote:
> Add a new callback, get_irq_reg, for regmap IRQ chips, to support devices
> with unusual register layouts. This is required in the rare cases where
> the offset of an IRQ register is not constant with respect to the base
> register. This is probably best illustrated with an example:
> 
>             mask    status
>     IRQ0    0x40    0x44
>     IRQ1    0x41    0x45
>     IRQ2    0x42    0x46
>     IRQ3    0x43    0x47
>     IRQ4    0x4a    0x4d
> 
> If we set mask_base = 0x40 and status_base = 0x44, the offsets of each
> register relative to the base are:
> 
>             mask    status
>     IRQ0    0       0
>     IRQ1    1       1
>     IRQ2    2       2
>     IRQ3    3       3
>     IRQ4    10      9
> 
> The existing mapping mechanisms can't include IRQ4 in the same irqchip
> as IRQ0-3 because the offset of IRQ4's register depends on which type
> of register we're asking for, ie. which base register is used.
> 
> The get_irq_reg callback allows drivers to specify an arbitrary mapping
> of (base register, register index) pairs to register addresses, instead
> of the default linear mapping "base_register + register_index". This
> allows unusual layouts, like the one above, to be handled using a single
> regmap IRQ chip.
> 
> The drawback is that when get_irq_reg is used, it's impossible to use
> bulk reads for status registers even if some of them are contiguous,
> because the mapping is opaque to regmap-irq. This should be acceptable
> for the case of a few infrequently-polled status registers.

This patch does two things:

1. Add a new callback `get_irq_reg`
2. Replace unmask_offset calculation with call to sub_irq_reg()

Could you please split the patch into two to better reflect this?

Thank you.

Guru Das.