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

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Message-Id: <65085C47-CDA8-4F8C-8307-C145F21F7D19@goldelico.com>
Date:   Wed, 25 Apr 2018 20:05:36 +0200
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Mark Rutland <mark.rutland@....com>,
        Alexandre Courbot <gnurou@...il.com>,
        Pawel Moll <pawel.moll@....com>,
        Ian Campbell <ijc+devicetree@...lion.org.uk>,
        Linus Walleij <linus.walleij@...aro.org>,
        kernel@...a-handheld.com,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Kumar Gala <galak@...eaurora.org>,
        Discussions about the Letux Kernel 
        <letux-kernel@...nphoenux.org>
Subject: Re: [Letux-kernel] [PATCH v3 2/4] gpio: pca953x: add register definitions for pcal6524 and fix address calculation

Hi Andy,

> Am 11.04.2018 um 07:00 schrieb H. Nikolaus Schaller <hns@...delico.com>:
> 
> 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.

Any news on this?

I am waiting for your advice before submitting v4 (with pending updates for the other patches).

> 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

BR and thanks,
Nikolaus