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Date:   Wed, 4 Nov 2020 14:02:12 +0100
From:   Andrew Lunn <andrew@lunn.ch>
To:     Lukasz Stelmach <l.stelmach@samsung.com>
Cc:     jim.cromie@gmail.com, Heiner Kallweit <hkallweit1@gmail.com>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Rob Herring <robh+dt@kernel.org>,
        Kukjin Kim <kgene@kernel.org>,
        Krzysztof Kozlowski <krzk@kernel.org>,
        Russell King <linux@armlinux.org.uk>, netdev@vger.kernel.org,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        linux-samsung-soc@vger.kernel.org,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        =?utf-8?Q?Bart=C5=82omiej_=C5=BBolnierkiewicz?= 
        <b.zolnierkie@samsung.com>
Subject: Re: [PATCH v5 3/5] net: ax88796c: ASIX AX88796C SPI Ethernet Adapter
 Driver
Message-ID: <20201104130212.GU933237@lunn.ch>
References: <20201104024211.GS933237@lunn.ch>
 <CGME20201104102048eucas1p1e3b29b66c497ee38656acf9ba5df10eb@eucas1p1.samsung.com>
 <dleftj361ps9sa.fsf%l.stelmach@samsung.com>
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> >> +static int
> >> +ax88796c_set_tunable(struct net_device *ndev, const struct ethtool_tunable *tuna,
> >> +		     const void *data)
> >> +{
> >> +	struct ax88796c_device *ax_local = to_ax88796c_device(ndev);
> >> +
> >> +	switch (tuna->id) {
> >> +	case ETHTOOL_SPI_COMPRESSION:
> >> +		if (netif_running(ndev))
> >> +			return -EBUSY;
> >> +		ax_local->capabilities &= ~AX_CAP_COMP;
> >> +		ax_local->capabilities |= *(u32 *)data ? AX_CAP_COMP : 0;
> >
> > You should probably validate here that data is 0 or 1. That is what
> > ax88796c_get_tunable() will return.
> >
> > It seems like this controls two hardware bits:
> >
> > SPICR_RCEN | SPICR_QCEN
> >
> > Maybe at some point it would make sense to allow these bits to be set
> > individually? If you never validate the tunable, you cannot make use
> > of other values to control the bits individually.
> 
> Good point. What is your recommendation for the userland facing
> interface, so that future changes will be least disruptive?

I would KISS and just validate data is 0 or 1, and leave it at that.
That then later gives you the option to have other values, if that is
ever interesting.

     Andrew