linux-kernel - Re: [PATCH 0/5] gnss: sirf: add support for w2sg0004 + lna

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Date:   Mon, 19 Nov 2018 20:05:23 +0100
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Andreas Kemnade <andreas@...nade.info>
Cc:     Johan Hovold <johan@...nel.org>, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        devicetree <devicetree@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Discussions about the Letux Kernel 
        <letux-kernel@...nphoenux.org>
Subject: Re: [PATCH 0/5] gnss: sirf: add support for w2sg0004 + lna

Hi,

> Am 19.11.2018 um 19:44 schrieb Andreas Kemnade <andreas@...nade.info>:
> 
> Hi,
> 
> On Mon, 19 Nov 2018 09:22:59 +0100
> "H. Nikolaus Schaller" <hns@...delico.com> wrote:
> 
>> Hi,
>> 
>>> Am 18.11.2018 um 22:57 schrieb Andreas Kemnade <andreas@...nade.info>:
>>> 
>>> Here is another chapter of the story to get gta04 gnss power
>>> management into the mainline kernel.
>>> There is a w2sg0004 without wakeup line in there, so power state
>>> can only be determined indirectly by looking at the serial data lines.
>>> Then there as also an lna which needs to be powered for real gps
>>> reception. That part needs probably more discussion, since it might
>>> be an idea to have it more generalized since it has nothing todo
>>> with the chip itself.  
>> 
>> On the other hand if we follow the "SoC is the spider in the net"
>> way of looking at DTS hierarchy, we have the uart as a child of the
>> SoC and the gnss receiver as a serdev child of the UART. The LNA
>> is even one step more distantly connected to the gnss. So it makes
>> sense to me to have it as a property/reference of the gnss chip's
>> DTS record which is a sibling of the compatible records. So the only
>> place where it can be reasonably processed is the driver.
>> 
> Or the lna is a child of the gnss receiver.

Well, this IMHO would assume the gnss receiver is a bus master...

> The whole thing
> should probably not be overdesigned, but it does not make sense that
> every gnss chip driver has some lna logic.
> Maybe the regulator should just be stored in the struct
> gnss_device and then drivers/gnss/core.c takes care.

Probably yes, but likely not difficult to refactor and generalize later
if users of other chips report a similar need. More important is to
get upstream support for the gta04 with this chip.

BR,
Nikolaus