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[78.83.68.78]) by smtp.gmail.com with ESMTPSA id cz17sm3199002edb.36.2021.08.15.01.54.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 15 Aug 2021 01:54:56 -0700 (PDT) Date: Sun, 15 Aug 2021 11:54:55 +0300 From: Petko Manolov To: Jakub Kicinski Cc: netdev@vger.kernel.org, paskripkin@gmail.com, stable@vger.kernel.org, davem@davemloft.net Subject: Re: [PATCH] net: usb: pegasus: ignore the return value from set_registers(); Message-ID: Mail-Followup-To: Jakub Kicinski , netdev@vger.kernel.org, paskripkin@gmail.com, stable@vger.kernel.org, davem@davemloft.net References: <20210812082351.37966-1-petko.manolov@konsulko.com> <20210813162439.1779bf63@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210813162439.1779bf63@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 21-08-13 16:24:39, Jakub Kicinski wrote: > On Thu, 12 Aug 2021 11:23:51 +0300 Petko Manolov wrote: > > The return value need to be either ignored or acted upon, otherwise 'deadstore' > > clang check would yell at us. I think it's better to just ignore what this > > particular call of set_registers() returns. The adapter defaults are sane and > > it would be operational even if the register write fail. > > > > Signed-off-by: Petko Manolov > > --- > > drivers/net/usb/pegasus.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/drivers/net/usb/pegasus.c b/drivers/net/usb/pegasus.c > > index 652e9fcf0b77..49cfc720d78f 100644 > > --- a/drivers/net/usb/pegasus.c > > +++ b/drivers/net/usb/pegasus.c > > @@ -433,7 +433,7 @@ static int enable_net_traffic(struct net_device *dev, struct usb_device *usb) > > data[2] = loopback ? 0x09 : 0x01; > > > > memcpy(pegasus->eth_regs, data, sizeof(data)); > > - ret = set_registers(pegasus, EthCtrl0, 3, data); > > + set_registers(pegasus, EthCtrl0, 3, data); > > > > if (usb_dev_id[pegasus->dev_index].vendor == VENDOR_LINKSYS || > > usb_dev_id[pegasus->dev_index].vendor == VENDOR_LINKSYS2 || > > This one is not added by the recent changes as I initially thought, > the driver has always checked this return value. The recent changes > did this: > > ret = set_registers(pegasus, EthCtrl0, 3, data); > > if (usb_dev_id[pegasus->dev_index].vendor == VENDOR_LINKSYS || > usb_dev_id[pegasus->dev_index].vendor == VENDOR_LINKSYS2 || > usb_dev_id[pegasus->dev_index].vendor == VENDOR_DLINK) { > u16 auxmode; > - read_mii_word(pegasus, 0, 0x1b, &auxmode); > + ret = read_mii_word(pegasus, 0, 0x1b, &auxmode); > + if (ret < 0) > + goto fail; > auxmode |= 4; > write_mii_word(pegasus, 0, 0x1b, &auxmode); > } > > + return 0; > +fail: > + netif_dbg(pegasus, drv, pegasus->net, "%s failed\n", __func__); > return ret; > } > > now the return value of set_registeres() is ignored. > > Seems like a better fix would be to bring back the error checking, > why not? Mostly because for this particular adapter checking the read failure makes much more sense than write failure. Checking the return value of set_register(s) is often usless because device's default register values are sane enough to get a working ethernet adapter even without much prodding. There are exceptions, though, one of them being set_ethernet_addr(). You could read the discussing in the netdev ML, but the essence of it is that set_ethernet_addr() should not give up if set_register(s) fail. Instead, the driver should assign a valid, even if random, MAC address. It is much the same situation with enable_net_traffic() - it should continue regardless. There are two options to resolve this: a) remove the error check altogether; b) do the check and print a debug message. I prefer a), but i am also not strongly opposed to b). Comments? > Please remember to add a fixes tag. Will do. cheers, Petko