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

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Date:   Thu, 26 Apr 2018 13:06:06 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     "H. Nikolaus Schaller" <hns@...delico.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

On Wed, Apr 25, 2018 at 9:05 PM, H. Nikolaus Schaller <hns@...delico.com> wrote:
>> Am 11.04.2018 um 07:00 schrieb H. Nikolaus Schaller <hns@...delico.com>:
>>> 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.

I actually think it would be even more patches:
 - move to hex from dec
 - add new definitions for PCAL953x
 - append new code for registers (see below)
 - add definitions for PCAL6524

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

So, what about something like:

--- 8< --- 8< ---
#define PCAL953X_GPIO_MASK GENMASK(5,0) // this makes sense even for
your initial solution

int bank_shift = fls((chip->gpio_chip.ngpio - 1) / BANK_SZ);
int addr = (reg & PCAL953X_GPIO_MASK) << bank_shift;
int pinctrl = (reg & ~PCAL953X_GPIO_MASK) << 1;

return i2c_smbus_write_i2c_block_data(chip->client,
                                             pinctrl | addr  | REG_ADDR_AI,
                                             NBANK(chip), val);

// similar for read.

--- 8< --- 8< ---

Keep in mind your solution has a bug for registers starting from 0x30.

-- 
With Best Regards,
Andy Shevchenko