netdev - Re: [PATCH v3 1/2] Driver core: add bus_find_device_by

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Date:   Wed, 10 Oct 2018 08:19:06 +0530
From:   Silesh C V <svellattu@...sta.com>
To:     Wolfram Sang <wsa@...-dreams.de>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-i2c@...r.kernel.org, linux-rdma@...r.kernel.org,
        netdev@...r.kernel.org, devicetree@...r.kernel.org,
        linux-spi@...r.kernel.org,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Lijun Ou <oulijun@...wei.com>,
        "Wei Hu(Xavier)" <xavier.huwei@...wei.com>,
        Yisen Zhuang <yisen.zhuang@...wei.com>,
        Salil Mehta <salil.mehta@...wei.com>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Mark Brown <broonie@...nel.org>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH v3 1/2] Driver core: add bus_find_device_by_fwnode

Hello Wolfram,

On Tue, Oct 9, 2018 at 4:32 PM Wolfram Sang <wsa@...-dreams.de> wrote:
>
> On Tue, Oct 09, 2018 at 03:47:24PM +0530, Silesh C V wrote:
> > Some drivers need to find the device on a bus having a specific firmware
> > node. Currently, such drivers have their own implementations to do this.
> > Provide a helper similar to bus_find_device_by_name so that each driver
> > does not have to reinvent this.
> >
> > Signed-off-by: Silesh C V <svellattu@...sta.com>
>
> Looks good in general, however:
>
> We recently had this discussion in I2C world about using the parent if
> the (logical) device has a NULL fw_node [1]. I don't know if the other
> subsystems you modify use logical devices as well? If no, it seems we
> need an additional check for the parent in the I2C core only. If yes,
> this might be considered in your patchset?

We can add an additional check for dev_fwnode(dev->parent) if match
for dev_fwnode(dev) fails in match_fwnode callback. Please correct me
if I am wrong. But then, we will be doing these two comparisons for
each device (until a match is found) on a bus for a bus_find_device
iteration(mostly unnecessarily because I could not find any "match
node" callbacks (for bus_find_device) currently doing this). So,
wouldn't it be better to add this check in exceptional cases (like in
the case of I2C) in the respective subsystems itself ?

Thanks,
Silesh