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From: Russell King - ARM Linux admin <linux@armlinux.org.uk>
To: Andrew Lunn <andrew@lunn.ch>
Cc: "Pali Rohár" <pali@kernel.org>,
	"David S. Miller" <davem@davemloft.net>,
	"Jakub Kicinski" <kuba@kernel.org>,
	"Thomas Schreiber" <tschreibe@gmail.com>,
	"Heiner Kallweit" <hkallweit1@gmail.com>,
	"Marek Behún" <kabel@kernel.org>,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 1/3] net: sfp: add workaround for Realtek RTL8672 and RTL9601C chips
Date: Thu, 7 Jan 2021 19:45:49 +0000	[thread overview]
Message-ID: <20210107194549.GR1551@shell.armlinux.org.uk> (raw)
In-Reply-To: <X/dCm1fK9jcjs4XT@lunn.ch>

On Thu, Jan 07, 2021 at 06:19:23PM +0100, Andrew Lunn wrote:
> > -static int sfp_quirk_i2c_block_size(const struct sfp_eeprom_base *base)
> > +static bool sfp_id_needs_byte_io(struct sfp *sfp, void *buf, size_t len)
> >  {
> > -	if (!memcmp(base->vendor_name, "VSOL            ", 16))
> > -		return 1;
> > -	if (!memcmp(base->vendor_name, "OEM             ", 16) &&
> > -	    !memcmp(base->vendor_pn,   "V2801F          ", 16))
> > -		return 1;
> > +	size_t i, block_size = sfp->i2c_block_size;
> >  
> > -	/* Some modules can't cope with long reads */
> > -	return 16;
> > -}
> > +	/* Already using byte IO */
> > +	if (block_size == 1)
> > +		return false;
> 
> This seems counter intuitive. We don't need byte IO because we are
> doing btye IO? Can we return True here?

It is counter-intuitive, but as this is indicating whether we need to
switch to byte IO, if we're already doing byte IO, then we don't need
to switch.

> > -static void sfp_quirks_base(struct sfp *sfp, const struct sfp_eeprom_base *base)
> > -{
> > -	sfp->i2c_block_size = sfp_quirk_i2c_block_size(base);
> > +	for (i = 1; i < len; i += block_size) {
> > +		if (memchr_inv(buf + i, '\0', block_size - 1))
> > +			return false;
> > +	}
> 
> Is the loop needed?

I think you're not reading the code very well. It checks for bytes at
offset 1..blocksize-1, blocksize+1..2*blocksize-1, etc are zero. It
does _not_ check that byte 0 or the byte at N*blocksize is zero - these
bytes are skipped. In other words, the first byte of each transfer can
be any value. The other bytes of the _entire_ ID must be zero.

> I also wonder if on the last iteration of the loop you go passed the
> end of buf? Don't you need a min(block_size -1, len - i) or
> similar?

The ID is 64 bytes long, and is fixed. block_size could be a non-power
of two, but that is highly unlikely. block_size will never be larger
than 16 either.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!

  parent reply	other threads:[~2021-01-07 19:47 UTC|newest]

Thread overview: 78+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-30 15:47 [PATCH 0/4] net: sfp: add support for GPON RTL8672/RTL9601C and Ubiquiti U-Fiber Pali Rohár
2020-12-30 15:47 ` [PATCH 1/4] net: sfp: add workaround for Realtek RTL8672 and RTL9601C chips Pali Rohár
2020-12-30 16:10   ` Russell King - ARM Linux admin
2020-12-30 16:56     ` Pali Rohár
2020-12-30 17:05       ` Russell King - ARM Linux admin
2020-12-30 17:13         ` Andrew Lunn
2020-12-30 17:43           ` Pali Rohár
2020-12-30 19:09             ` Russell King - ARM Linux admin
2020-12-30 19:49               ` Andrew Lunn
2020-12-31 12:14               ` Pali Rohár
2020-12-31 15:09                 ` Andrew Lunn
2020-12-31 15:40                   ` Pali Rohár
2020-12-31 15:30                 ` Andrew Lunn
2020-12-31 17:00                   ` Pali Rohár
2020-12-31 17:13                     ` Andrew Lunn
2021-01-02  1:49                       ` Pali Rohár
2021-01-03  2:25                         ` Thomas Schreiber
2021-01-03  2:41                           ` Pali Rohár
2021-01-06 14:55                             ` Pali Rohár
2021-01-06 15:21                               ` Russell King - ARM Linux admin
2021-01-06 15:23                                 ` Russell King - ARM Linux admin
2021-01-06 15:27                                   ` Russell King - ARM Linux admin
2021-01-06 15:35                                     ` Pali Rohár
2020-12-30 19:30             ` Andrew Lunn
2020-12-30 19:39               ` Russell King - ARM Linux admin
2020-12-30 17:31         ` Pali Rohár
2020-12-30 19:18           ` Russell King - ARM Linux admin
2020-12-30 15:47 ` [PATCH 2/4] net: sfp: allow to use also SFP modules which are detected as SFF Pali Rohár
2020-12-30 16:11   ` Russell King - ARM Linux admin
2020-12-30 17:06     ` Pali Rohár
2020-12-30 17:27       ` Marek Behún
2020-12-30 19:12         ` Russell King - ARM Linux admin
2020-12-31 13:52           ` Pali Rohár
2020-12-30 15:47 ` [PATCH 3/4] net: sfp: assume that LOS is not implemented if both LOS normal and inverted is set Pali Rohár
2020-12-30 16:13   ` Russell King - ARM Linux admin
2020-12-30 16:57     ` Pali Rohár
2020-12-30 17:06       ` Russell King - ARM Linux admin
2020-12-30 17:17         ` Andrew Lunn
2020-12-30 17:32           ` Pali Rohár
2020-12-30 15:47 ` [PATCH 4/4] net: sfp: add mode quirk for GPON module Ubiquiti U-Fiber Instant Pali Rohár
2021-01-06 15:37 ` [PATCH v2 0/3] net: sfp: add support for GPON RTL8672/RTL9601C and Ubiquiti U-Fiber Pali Rohár
2021-01-06 15:37   ` [PATCH v2 1/3] net: sfp: add workaround for Realtek RTL8672 and RTL9601C chips Pali Rohár
2021-01-07  2:02     ` Andrew Lunn
2021-01-07  9:08       ` Pali Rohár
2021-01-07 17:19     ` Andrew Lunn
2021-01-07 17:40       ` Russell King - ARM Linux admin
2021-01-07 19:18         ` Pali Rohár
2021-01-07 19:17       ` Pali Rohár
2021-01-07 19:45       ` Russell King - ARM Linux admin [this message]
2021-01-07 20:21         ` Marek Behún
2021-01-08  0:49           ` Pali Rohár
2021-01-06 15:37   ` [PATCH v2 2/3] net: sfp: assume that LOS is not implemented if both LOS normal and inverted is set Pali Rohár
2021-01-07 16:54     ` Andrew Lunn
2021-01-09 15:46       ` Russell King - ARM Linux admin
2021-01-09 15:54         ` Andrew Lunn
2021-01-09 16:27           ` Russell King - ARM Linux admin
2021-01-09 19:14         ` Pali Rohár
2021-01-09 23:19           ` Russell King - ARM Linux admin
2021-01-09 23:50             ` Pali Rohár
2021-01-06 15:37   ` [PATCH v2 3/3] net: sfp: add mode quirk for GPON module Ubiquiti U-Fiber Instant Pali Rohár
2021-01-07 16:51     ` Andrew Lunn
2021-01-11 11:39 ` [PATCH v3 0/2] net: sfp: add support for GPON RTL8672/RTL9601C and Ubiquiti U-Fiber Pali Rohár
2021-01-11 11:39   ` [PATCH v3 1/2] net: sfp: add workaround for Realtek RTL8672 and RTL9601C chips Pali Rohár
2021-01-11 15:28     ` Marek Behún
2021-01-11 11:39   ` [PATCH v3 2/2] net: sfp: add mode quirk for GPON module Ubiquiti U-Fiber Instant Pali Rohár
2021-01-11 15:32     ` Marek Behún
2021-01-12 13:33   ` [PATCH v3 0/2] net: sfp: add support for GPON RTL8672/RTL9601C and Ubiquiti U-Fiber Pali Rohár
2021-01-18  9:34   ` Pali Rohár
2021-01-25 14:09     ` Pali Rohár
2021-01-25 14:16       ` Russell King - ARM Linux admin
2021-01-25 14:23         ` Pali Rohár
2021-01-25 14:42           ` Russell King - ARM Linux admin
2021-01-25 14:47             ` Pali Rohár
2021-01-25 15:41               ` Andrew Lunn
2021-01-25 15:02 ` [PATCH v4 " Pali Rohár
2021-01-25 15:02   ` [PATCH v4 1/2] net: sfp: add workaround for Realtek RTL8672 and RTL9601C chips Pali Rohár
2021-01-25 15:02   ` [PATCH v4 2/2] net: sfp: add mode quirk for GPON module Ubiquiti U-Fiber Instant Pali Rohár
2021-01-28 21:50   ` [PATCH v4 0/2] net: sfp: add support for GPON RTL8672/RTL9601C and Ubiquiti U-Fiber patchwork-bot+netdevbpf

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