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

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Message-ID: <20230926-action-sludge-ec8e51fdd6d4@spud>
Date:   Tue, 26 Sep 2023 10:02:04 +0100
From:   Conor Dooley <conor@...nel.org>
To:     yang tylor <tylor_yang@...ax.corp-partner.google.com>
Cc:     Conor Dooley <conor.dooley@...rochip.com>,
        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>,
        wuxy23@...ovo.com, luolm1@...ovo.com,
        hung poyu <poyu_hung@...ax.corp-partner.google.com>
Subject: Re: [PATCH V2 1/2] dt-bindings: input: Introduce Himax HID-over-SPI
 device

On Mon, Sep 25, 2023 at 06:16:29PM +0800, yang tylor wrote:
> On Mon, Sep 25, 2023 at 4:41 PM Conor Dooley <conor.dooley@...rochip.com> wrote:
> >
> > 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.
> Yep.
> 
> > 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.

> We have a default prefix firmware name(like himax_xxxx.bin) in the driver code.

How do you intend generating the name of the firmware file? I assume the
same firmware doesn't work on every IC, so you'll need to pick a
different one depending on the compatible?

> So we'll look for it when no-flash-flag is specified. In our experience,
> forcing a prefix firmware name helps the user to aware what firmware
> they are dealing with.

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