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From: Andrew Lunn <andrew@lunn.ch>
To: "Pali Rohár" <pali@kernel.org>
Cc: "Russell King - ARM Linux admin" <linux@armlinux.org.uk>,
	"Heiner Kallweit" <hkallweit1@gmail.com>,
	"David S. Miller" <davem@davemloft.net>,
	"Jakub Kicinski" <kuba@kernel.org>,
	"Marek Behún" <kabel@kernel.org>,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/4] net: sfp: add workaround for Realtek RTL8672 and RTL9601C chips
Date: Thu, 31 Dec 2020 16:09:25 +0100	[thread overview]
Message-ID: <X+3ppQhbjCGFzs6P@lunn.ch> (raw)
In-Reply-To: <20201231121410.2xlxtyqjelrlysd2@pali>

On Thu, Dec 31, 2020 at 01:14:10PM +0100, Pali Rohár wrote:
> On Wednesday 30 December 2020 19:09:58 Russell King - ARM Linux admin wrote:
> > On Wed, Dec 30, 2020 at 06:43:07PM +0100, Pali Rohár wrote:
> > > On Wednesday 30 December 2020 18:13:15 Andrew Lunn wrote:
> > > > Hi Pali
> > > > 
> > > > I have to agree with Russell here. I would rather have no diagnostics
> > > > than untrustable diagnostics.
> > > 
> > > Ok!
> > > 
> > > So should we completely skip hwmon_device_register_with_info() call
> > > if (i2c_block_size < 2) ?
> > 
> > I don't think that alone is sufficient - there's also the matter of
> > ethtool -m which will dump that information as well, and we don't want
> > to offer it to userspace in an unreliable form.
> 
> Any idea/preference how to disable access to these registers?
> 
> > For reference, here is what SFF-8472 which defines the diagnostics, says
> > about this:
> > 
> >   To guarantee coherency of the diagnostic monitoring data, the host is
> >   required to retrieve any multi-byte fields from the diagnostic
> >   monitoring data structure (IE: Rx Power MSB - byte 104 in A2h, Rx Power
> >   LSB - byte 105 in A2h) by the use of a single two-byte read sequence
> >   across the two-wire interface interface.
> > 
> >   The transceiver is required to ensure that any multi-byte fields which
> >   are updated with diagnostic monitoring data (e.g. Rx Power MSB - byte
> >   104 in A2h, Rx Power LSB - byte 105 in A2h) must have this update done
> >   in a fashion which guarantees coherency and consistency of the data. In
> >   other words, the update of a multi-byte field by the transceiver must
> >   not occur such that a partially updated multi-byte field can be
> >   transferred to the host. Also, the transceiver shall not update a
> >   multi-byte field within the structure during the transfer of that
> >   multi-byte field to the host, such that partially updated data would be
> >   transferred to the host.
> > 
> > The first paragraph is extremely definitive in how these fields shall
> > be read atomically - by a _single_ two-byte read sequence. From what
> > you are telling us, these modules do not support that. Therefore, by
> > definition, they do *not* support proper and reliable reporting of
> > diagnostic data, and are non-conformant with the SFP MSAs.
> > 
> > So, they are basically broken, and the diagnostics can't be used to
> > retrieve data that can be said to be useful.
> 
> I agree they are broken. We really should disable access to those 16bit
> registers.
> 
> Anyway here is "datasheet" to some CarlitoxxPro SFP:
> https://www.docdroid.net/hRsJ560/cpgos03-0490v2-datasheet-10-pdf
> 
> And on page 10 is written:
> 
>     The I2C system can support the mode of random address / single
>     byteread which conform to SFF-8431.
> 
> Which seems to be wrong.

Searching around, i found:

http://read.pudn.com/downloads776/doc/3073304/RTL9601B-CG_Datasheet.pdf

It has two i2c busses, a master and a slave. The master bus can do
multi-byte transfers. The slave bus description says nothing in words
about multi-byte transfers, but the diagram shows only single byte
transfers.

So any SFP based around this device is broken.

The silly thing is, it is reading/writing from a shadow SRAM. The CPU
is not directly involved in an I2C transaction. So it could easily
read multiple bytes from the SRAM and return them. But it would still
need a synchronisation method to handle writes from the CPU to the
SRAM, in order to make these word values safe.

      Andrew

  reply	other threads:[~2020-12-31 15:10 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 [this message]
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
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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