linux-kernel - Re: [PATCH v2 1/3] input: cygnus-update touchscreen dt node document

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Date:	Fri, 19 Feb 2016 11:43:50 +0530
From:	Raveendra Padasalagi <raveendra.padasalagi@...adcom.com>
To:	Rob Herring <robh@...nel.org>
Cc:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Russell King <linux@....linux.org.uk>,
	Arnd Bergmann <arnd@...db.de>, devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-input@...r.kernel.org,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Jonathan Richardson <jonathar@...adcom.com>,
	Jon Mason <jonmason@...adcom.com>,
	Florian Fainelli <f.fainelli@...il.com>,
	Anup Patel <anup.patel@...adcom.com>,
	Ray Jui <rjui@...adcom.com>,
	Scott Branden <sbranden@...adcom.com>,
	linux-kernel@...r.kernel.org, bcm-kernel-feedback-list@...adcom.com
Subject: Re: [PATCH v2 1/3] input: cygnus-update touchscreen dt node document

On Thu, Feb 18, 2016 at 8:06 PM, Rob Herring <robh@...nel.org> wrote:
> On Wed, Feb 17, 2016 at 03:13:44PM +0530, Raveendra Padasalagi wrote:
>> In Cygnus SOC touch screen controller registers are shared
>> with ADC and flex timer. Using readl/writel could lead to
>> race condition. So touch screen driver is enhanced to support
>>
>> 1. If touchscreen register's are not shared. Register access
>> is handled through readl/writel if "brcm,iproc-touchscreen"
>> compatible is provided in touchscreen dt node. This will help
>> for future SOC's if comes with dedicated touchscreen IP register's.
>>
>> 2. If touchscreen register's are shared with other IP's, register
>> access is handled through syscon framework API's to take care of
>> mutually exclusive access. This feature can be enabled by selecting
>> "brcm,iproc-touchscreen-syscon" compatible string in the touchscreen
>> dt node.
>>
>> Hence touchscreen dt node bindings document is updated to take care
>> of above changes in the touchscreen driver.
>>
>> Signed-off-by: Raveendra Padasalagi <raveendra.padasalagi@...adcom.com>
>> Reviewed-by: Ray Jui <ray.jui@...adcom.com>
>> Reviewed-by: Scott Branden <scott.branden@...adcom.com>
>> ---
>>  .../input/touchscreen/brcm,iproc-touchscreen.txt   | 57 +++++++++++++++++++---
>>  1 file changed, 51 insertions(+), 6 deletions(-)
>>
>> diff --git a/Documentation/devicetree/bindings/input/touchscreen/brcm,iproc-touchscreen.txt b/Documentation/devicetree/bindings/input/touchscreen/brcm,iproc-touchscreen.txt
>> index 34e3382..f530c25 100644
>> --- a/Documentation/devicetree/bindings/input/touchscreen/brcm,iproc-touchscreen.txt
>> +++ b/Documentation/devicetree/bindings/input/touchscreen/brcm,iproc-touchscreen.txt
>> @@ -1,12 +1,30 @@
>>  * Broadcom's IPROC Touchscreen Controller
>>
>>  Required properties:
>> -- compatible: must be "brcm,iproc-touchscreen"
>> -- reg: physical base address of the controller and length of memory mapped
>> -  region.
>> +- compatible: should be one of
>> +        "brcm,iproc-touchscreen"
>> +        "brcm,iproc-touchscreen-syscon"
>
> More specific and this is not how you do syscon. Either the block is or
> isn't. You can't have it both ways.

Existing driver has support for reg, if we modify now to support only syscon
then this driver will not work if some one wishes to use previous
kernel version's
dt and vice versa. Basically this breaks dt compatibility. Is that ok ?

>> +- ts_syscon: if "brcm,iproc-touchscreen-syscon" compatible string
>> +  is selected then "ts_syscon" is mandatory or else not required.
>> +  The "ts_syscon" is handler of syscon node defining physical base
>> +  address of the controller and length of memory mapped region.
>> +  If this property is selected please make sure MFD_SYSCON config
>> +  is enabled in the defconfig file.
>> +- reg: if "brcm,iproc-touchscreen" compatible string is selected
>> +  then "reg" property is mandatory or else not required.
>> +  The "reg" should be physical base address of the controller and
>> +  length of memory mapped region.
>
> I thought every chip to date is a syscon. Add reg support when you
> actually need it.

Since the existing driver has support for reg and now if we modify it to
support syscon only then we break the dt compatibility with previous kernel
versions. So keeping support for both will help to avoid dt
compatibility issues.

I will change the driver if you still think syscon only support is fine.
Let me know your opinion.

>>  - clocks:  The clock provided by the SOC to driver the tsc
>>  - clock-name:  name for the clock
>>  - interrupts: The touchscreen controller's interrupt
>> +- address-cells: Specify the number of u32 entries needed in child nodes.
>> +                 Should set to 1. This property is mandatory when
>> +                 "brcm,iproc-touchscreen-syscon" compatible string is selected
>> +                 or else not required.
>> +- size-cells: Specify number of u32 entries needed to specify child nodes size
>> +              in reg property. Should set to 1.This property is mandatory when
>> +              "brcm,iproc-touchscreen-syscon" compatible string is selected or
>> +              else not required.
>>
>>  Optional properties:
>>  - scanning_period: Time between scans. Each step is 1024 us.  Valid 1-256.
>> @@ -53,13 +71,40 @@ Optional properties:
>>  - touchscreen-inverted-x: X axis is inverted (boolean)
>>  - touchscreen-inverted-y: Y axis is inverted (boolean)
>>
>> -Example:
>> +Example 1: An example of touchscreen node with "brcm,iproc-touchscreen-syscon"
>> +           compatible string.
>> +
>> +     ts_adc_syscon: ts_adc_syscon@...80a6000 {
>> +             compatible = "syscon";
>> +             reg = <0x180a6000 0xc30>;
>> +     };
>>
>>       touchscreen: tsc@...80A6000 {
>
> Drop the '0x' and the node name should be touchscreen, not tsc.

I will address this in the next patch.

>> -             compatible = "brcm,iproc-touchscreen";
>> +             compatible = "brcm,iproc-touchscreen-syscon";
>>               #address-cells = <1>;
>>               #size-cells = <1>;
>> -             reg = <0x180A6000 0x40>;
>> +             ts_syscon = <&ts_adc_syscon>;
>> +             clocks = <&adc_clk>;
>> +             clock-names = "tsc_clk";
>> +             interrupts = <GIC_SPI 164 IRQ_TYPE_LEVEL_HIGH>;
>> +
>
>> +             scanning_period = <5>;
>> +             debounce_timeout = <40>;
>> +             settling_timeout = <7>;
>> +             touch_timeout = <10>;
>> +             average_data = <5>;
>> +             fifo_threshold = <1>;
>
> New properties?

No, These are existing properties.

>> +             /* Touchscreen is rotated 180 degrees. */
>> +             touchscreen-inverted-x;
>> +             touchscreen-inverted-y;
>> +     };
>> +
>> +Example 2: An example of touchscreen node with "brcm,iproc-touchscreen"
>> +          compatible string.
>> +
>> +     touchscreen: tsc@...80A6000 {
>> +             compatible = "brcm,iproc-touchscreen";
>> +             reg = <0x180a6000 0x40>;
>>               clocks = <&adc_clk>;
>>               clock-names = "tsc_clk";
>>               interrupts = <GIC_SPI 164 IRQ_TYPE_LEVEL_HIGH>;
>> --
>> 1.9.1
>>