linux-kernel - Re: [PATCH v3 2/4] gpio: pca953x: add register definitions for pcal6524 and fix address calculation

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Message-Id: <EDF7FA02-C79C-4ADF-A10C-F8C4DBFE5158@goldelico.com>
Date:   Wed, 11 Apr 2018 07:00:04 +0200
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Kumar Gala <galak@...eaurora.org>,
        Rob Herring <robh+dt@...nel.org>,
        Pawel Moll <pawel.moll@....com>,
        Mark Rutland <mark.rutland@....com>,
        Ian Campbell <ijc+devicetree@...lion.org.uk>,
        Linus Walleij <linus.walleij@...aro.org>,
        Alexandre Courbot <gnurou@...il.com>,
        devicetree <devicetree@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Discussions about the Letux Kernel 
        <letux-kernel@...nphoenux.org>, kernel@...a-handheld.com
Subject: Re: [PATCH v3 2/4] gpio: pca953x: add register definitions for pcal6524 and fix address calculation

Hi Andy,

> Am 10.04.2018 um 20:06 schrieb Andy Shevchenko <andy.shevchenko@...il.com>:
> 
> On Tue, Apr 10, 2018 at 7:07 PM, H. Nikolaus Schaller <hns@...delico.com> wrote:
>> PCAL chips ("L" seems to stand for "latched") have additional
>> registers starting at address 0x40 to control the latches,
>> interrupt mask, pull-up and pull down etc.
>> 
>> The constants are so far defined in a way that they fit for
>> the pcal9555a when shifted by the number of banks, i.e. multiplied
>> by 2.
>> 
>> Now the pcal6524 has 3 banks which means the relative offset
>> must be multiplied by 4 which gives a wrong result if not done
>> carefully, since the base offset is already included in the offset.
>> 
>> For the basic registers shared with all pca93xx/tca64xx chips
>> there is no such offset.
>> 
>> Therefore, we add code to adjust the register number for exended
>> registers to the 24 bit accessor functions.
>> 
>> And we add additional register offset constants (not yet used by
>> the driver code) which are specific to the pcal6524.
>> 
> 
> First of all, as I said, please split this to two patches. Don't mix the things.

Ok. Queued for v4.

> 
> 
>> +       /* adjust register address for pcal6524 */
>> +       if (reg >= PCAL953X_OUT_STRENGTH)
>> +               reg -= PCAL953X_OUT_STRENGTH >> 1;
>> +
> 
> Give me some days to think about it.

No problem. I'll wait with v4.

The only alternative I would see is to add new accessor function
pointers for the extended registers and have 0x00 based offsets,
but that is IMHO more ugly.

BR and thanks,
Nikolaus