linux-kernel - Re: [PATCH V2 1/2] dt-bindings: input: Introduce Himax HID-over-SPI device

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Message-ID: <20230925-cod-vacancy-08dc8d88f90e@wendy>
Date:   Mon, 25 Sep 2023 09:41:14 +0100
From:   Conor Dooley <conor.dooley@...rochip.com>
To:     yang tylor <tylor_yang@...ax.corp-partner.google.com>
CC:     Conor Dooley <conor@...nel.org>, <dmitry.torokhov@...il.com>,
        <robh+dt@...nel.org>, <krzysztof.kozlowski+dt@...aro.org>,
        <conor+dt@...nel.org>, <jikos@...nel.org>,
        <benjamin.tissoires@...hat.com>, <linux-input@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <poyuan_chang@...ax.corp-partner.google.com>,
        <hbarnor@...omium.org>,
        "jingyliang@...omium.org" <jingyliang@...omium.org>
Subject: Re: [PATCH V2 1/2] dt-bindings: input: Introduce Himax HID-over-SPI
 device

On Mon, Sep 25, 2023 at 09:44:21AM +0800, yang tylor wrote:
> On Fri, Sep 22, 2023 at 11:31 PM Conor Dooley <conor@...nel.org> wrote:
> >
> > On Fri, Sep 22, 2023 at 05:43:54PM +0800, yang tylor wrote:
> > > On Fri, Sep 22, 2023 at 5:22 PM Conor Dooley <conor@...nel.org> wrote:
> > > >
> > > > On Fri, Sep 22, 2023 at 03:56:25PM +0800, yang tylor wrote:
> > > > > On Tue, Sep 19, 2023 at 7:09 PM Conor Dooley <conor@...nel.org> wrote:
> > > > > > On Tue, Sep 19, 2023 at 05:31:29PM +0800, yang tylor wrote:
> > > >
> > > > > > > The behavior of "himax,boot_time_fw_upgrade" seems not stable and
> > > > > > > should be removed. "himax,fw_in_flash", I use the kernel config for
> > > > > > > user to select.
> > > > > >
> > > > > > That seems like a bad idea, we want to be able to build one kernel that
> > > > > > works for all hardware at the same time.
> > > > > >
> > > > > I see, so I should take that back?
> > > > > I'll explain more about it.
> > > >
> > > > Are there particular ICs where the firmware would always be in flash and
> > > > others where it would never be? Or is this a choice made by the board or
> > > > system designer?
> > > >
> > > Most cases it's about the system designer's decision. But some ICs may be forced
> > > to use flash because of its architecture(multiple IC inside, need to
> > > load firmware to
> > > multiple IC's sram by master IC). But if there is no limitation on
> > > this part, most system
> > > designers will prefer flashless.
> >
> > Forgive me if I am not understanding correctly, there are some ICs that
> > will need to load the firmware from flash and there are some where it
> > will be a decision made by the designer of the board. Is the flash part
> > of the IC or is it an external flash chip?
> >
> 
> Both are possible, it depends on the IC type. For TDDI, the IC is long
> and thin, placed on panel PCB, flash will be located at the external
> flash chip. For the OLED TP, IC is usually placed at FPC and its flash
> is embedded, thus the IC size is large compared to TDDI. But from the
> driver's perspective either external flash or embedded flash, the IC
> itself will load firmware from flash automatically when reset pin is
> released. Only if firmware is loading from the host storage system,
> the driver needs to operate the IC in detail.


Since there are ICs that can use the external flash or have it loaded
from the host, it sounds like you do need a property to differentiate
between those cases.
Is it sufficient to just set the firmware-name property for these cases?
If the property exists, then you know you need to load firmware & what
its name is. If it doesn't, then the firmware either isn't needed or
will be automatically loaded from the external flash.

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