linux-kernel - Re: [tpmdd-devel] [PATCH 1/2] tpm: Apply an adapterlimit for retransmission.

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Date:   Mon, 27 Feb 2017 20:12:45 +0100
From:   Wolfram Sang <wsa@...-dreams.de>
To:     Enric Balletbo Serra <eballetbo@...il.com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        Peter Huewe <peterhuewe@....de>,
        Marcel Selhorst <tpmdd@...horst.net>, apronin@...gle.com,
        tpmdd-devel@...ts.sourceforge.net,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [tpmdd-devel] [PATCH 1/2] tpm: Apply an adapterlimit for
 retransmission.

Hi,

> >> > Rather than trying small and smaller transfers, would it not be better
> >> > to get the i2c core to expose the quirk info about transfer limits?
> >> >
> >>
> >> Sounds a good idea to me, I guess the quirk info can be accessed with
> >>
> >>   tpm_dev.client->adapter->quirks->max_read_len
> >>
> >> so I think we don't need to touch the i2c core. I'll propose a second version of the patch.
> >
> > Hi Enric
> >
> > You should probably ask Wolfram Sang <wsa@...-dreams.de>, the i2c
> > subsystem maintainer. He may prefer adding an API call.

Thanks for pointing me to this thread.

I understand it looks tempting to use the quirks struct directly, but I
don't think this is the proper solution. Quirks are complex and and to
determine which one finally applies, you need all the logic encoded in
i2c_check_for_quirks(). Which already gets called on every transfer.

So, my suggestion would be to simply fall back to a sane minimum when
the maximum failed. 32 (I2C_SMBUS_BLOCK_MAX) should be a good choice.

BTW I noted that the original patch checks for -EINVAL. The core returns
-EOPNOTSUPP, though. So, a) the patch needs to be adapted and b) it
looks the i2c host driver returning -EINVAL could be converted to use
the quirk infrastructure? Which driver is it?

Regards,

   Wolfram


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