linux-kernel - Re: [PATCH v3 4/4] tpm: add driver for cr50 on SPI

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Date:   Thu, 15 Aug 2019 16:00:11 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     Peter Huewe <peterhuewe@....de>,
        Andrey Pronin <apronin@...omium.org>,
        linux-kernel@...r.kernel.org, linux-integrity@...r.kernel.org,
        Duncan Laurie <dlaurie@...omium.org>,
        Jason Gunthorpe <jgg@...pe.ca>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Guenter Roeck <groeck@...omium.org>,
        Alexander Steffen <Alexander.Steffen@...ineon.com>
Subject: Re: [PATCH v3 4/4] tpm: add driver for cr50 on SPI

On Mon, Aug 12, 2019 at 01:46:35PM -0700, Stephen Boyd wrote:
> Quoting Jarkko Sakkinen (2019-08-09 13:31:04)
> > On Tue, 2019-08-06 at 15:07 -0700, Stephen Boyd wrote:
> > > From: Andrey Pronin <apronin@...omium.org>
> > > 
> > > Add TPM2.0 PTP FIFO compatible SPI interface for chips with Cr50
> > > firmware. The firmware running on the currently supported H1
> > > Secure Microcontroller requires a special driver to handle its
> > > specifics:
> > > 
> > >  - need to ensure a certain delay between spi transactions, or else
> > >    the chip may miss some part of the next transaction;
> > >  - if there is no spi activity for some time, it may go to sleep,
> > >    and needs to be waken up before sending further commands;
> > >  - access to vendor-specific registers.
> > 
> > Which Chromebook models have this chip?
> 
> Pretty much all Chromebooks released in the last year or two have this
> chip in them. I don't have an exhaustive list, but you can usually check
> this by putting your device into dev mode and then looking at the driver
> attached to the TPM device in sysfs or by grepping the dmesg output for
> cr50.
> 
> > 
> > If I had an access to one, how do I do kernel testing with it i.e.
> > how do I get it to boot initramfs and bzImage from a USB stick?
> > 
> > 
> 
> You can follow the developer guide[1] and build a USB image for the
> board you have. You can usually checkout the latest upstream kernel in
> place of where the kernel is built from in the chroot, typically
> ~/trunk/src/third_party/kernel/<version number>. The build should pick
> up that it's an upstream tree and try to use some default defconfig.
> This driver isn't upstream yet, so you may need to enable it in the
> defconfig, located in
> ~/trunk/src/third_party/chromiumos-overlay/eclass/cros-kernel/ so that
> the driver is actually built. After that, use 'cros flash' to flash the
> new kernel image to your USB stick and boot from USB with 'ctrl+u' and
> you should be on your way to chromeos kernel testing.
> 
> [1] https://chromium.googlesource.com/chromiumos/docs/+/master/developer_guide.md

Hey, thanks for info! I'll see if I can get my hands on one.

/Jarkko