netdev - Re: [PATCH net-next] net: sfp: VSOL V2801F / CarlitoxxPro CPGOS03-0490 v2.0 workaround

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Message-ID: <20201124094314.GC1551@shell.armlinux.org.uk>
Date:   Tue, 24 Nov 2020 09:43:14 +0000
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Heiner Kallweit <hkallweit1@...il.com>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        Jakub Kicinski <kuba@...nel.org>
Subject: Re: [PATCH net-next] net: sfp: VSOL V2801F / CarlitoxxPro
 CPGOS03-0490 v2.0 workaround

On Tue, Nov 24, 2020 at 01:20:21AM +0100, Andrew Lunn wrote:
> > @@ -335,10 +336,19 @@ static int sfp_i2c_read(struct sfp *sfp, bool a2, u8 dev_addr, void *buf,
> >  			size_t len)
> >  {
> >  	struct i2c_msg msgs[2];
> > -	u8 bus_addr = a2 ? 0x51 : 0x50;
> > +	size_t block_size;
> >  	size_t this_len;
> > +	u8 bus_addr;
> >  	int ret;
> >  
> > +	if (a2) {
> > +		block_size = 16;
> > +		bus_addr = 0x51;
> 
> Hi Russell, Thomas
> 
> Does this man the diagnostic page can be read 16 bytes at a time, even
> when the other page has to be 1 bytes at a time? That seems rather
> odd. Or is the diagnostic page not implemented in these SFPs?

SFF8472 requires that multibyte values are read using sequential
reads. So we can't use single byte reads to read a multibyte value -
it's just not atomic.

-- 
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