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Date: Tue, 24 Nov 2020 10:14:22 -0300
From: Ezequiel Garcia <ezequiel@...labora.com>
To: Jarkko Sakkinen <jarkko@...nel.org>,
Adrian Ratiu <adrian.ratiu@...labora.com>
Cc: linux-integrity@...r.kernel.org, Peter Huewe <peterhuewe@....de>,
Jason Gunthorpe <jgg@...pe.ca>,
Helen Koike <helen.koike@...labora.com>,
Duncan Laurie <dlaurie@...omium.org>,
Stephen Boyd <swboyd@...omium.org>, kernel@...labora.com,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] char: tpm: add i2c driver for cr50
Hi Jarkko,
Thanks for your review.
On Tue, 2020-11-24 at 00:06 +0200, Jarkko Sakkinen wrote:
> On Fri, Nov 20, 2020 at 07:23:45PM +0200, Adrian Ratiu wrote:
> > From: "dlaurie@...omium.org" <dlaurie@...omium.org>
> >
> > Add TPM 2.0 compatible I2C interface for chips with cr50 firmware.
> >
> > The firmware running on the currently supported H1 MCU requires a
> > special driver to handle its specific protocol, and this makes it
> > unsuitable to use tpm_tis_core_* and instead it must implement the
> > underlying TPM protocol similar to the other I2C TPM drivers.
> >
> > - All 4 byes of status register must be read/written at once.
> > - FIFO and burst count is limited to 63 and must be drained by AP.
> > - Provides an interrupt to indicate when read response data is ready
> > and when the TPM is finished processing write data.
> >
> > This driver is based on the existing infineon I2C TPM driver, which
> > most closely matches the cr50 i2c protocol behavior.
> >
> > Cc: Helen Koike <helen.koike@...labora.com>
> > Signed-off-by: Duncan Laurie <dlaurie@...omium.org>
> > [swboyd@...omium.org: Depend on i2c even if it's a module, replace
> > boilier plate with SPDX tag, drop asm/byteorder.h include, simplify
> > return from probe]
> > Signed-off-by: Stephen Boyd <swboyd@...omium.org>
> > Signed-off-by: Fabien Lahoudere <fabien.lahoudere@...labora.com>
> > Signed-off-by: Adrian Ratiu <adrian.ratiu@...labora.com>
> > ---
> > Changes in v2:
> > - Various small fixes all over (reorder includes, MAX_BUFSIZE, comments, etc)
> > - Reworked return values of i2c_wait_tpm_ready() to fix timeout mis-handling
> > so ret == 0 now means success, the wait period jiffies is ignored because that
> > number is meaningless and return a proper timeout error in case jiffies == 0.
> > - Make i2c default to 1 message per transfer (requested by Helen)
> > - Move -EIO error reporting to transfer function to cleanup transfer() itself
> > and its R/W callers
> > - Remove magic value hardcodings and introduce enum force_release.
> >
> > v1 posted at https://lkml.org/lkml/2020/2/25/349
> >
> > Applies on next-20201120, tested on Chromebook EVE.
> > ---
> > drivers/char/tpm/Kconfig | 10 +
> > drivers/char/tpm/Makefile | 2 +
> > drivers/char/tpm/tpm_tis_i2c_cr50.c | 768 ++++++++++++++++++++++++++++
> > 3 files changed, 780 insertions(+)
> > create mode 100644 drivers/char/tpm/tpm_tis_i2c_cr50.c
> >
> > diff --git a/drivers/char/tpm/Kconfig b/drivers/char/tpm/Kconfig
> > index a18c314da211..4308f9ca7a43 100644
> > --- a/drivers/char/tpm/Kconfig
> > +++ b/drivers/char/tpm/Kconfig
> > @@ -86,6 +86,16 @@ config TCG_TIS_SYNQUACER
> > To compile this driver as a module, choose M here;
> > the module will be called tpm_tis_synquacer.
> >
> > +config TCG_TIS_I2C_CR50
> > + tristate "TPM Interface Specification 2.0 Interface (I2C - CR50)"
> > + depends on I2C
> > + select TCG_CR50
> > + help
> > + This is a driver for the Google cr50 I2C TPM interface which is a
> > + custom microcontroller and requires a custom i2c protocol interface
> > + to handle the limitations of the hardware. To compile this driver
> > + as a module, choose M here; the module will be called tcg_tis_i2c_cr50.
> > +
> > config TCG_TIS_I2C_ATMEL
> > tristate "TPM Interface Specification 1.2 Interface (I2C - Atmel)"
> > depends on I2C
> > diff --git a/drivers/char/tpm/Makefile b/drivers/char/tpm/Makefile
> > index 84db4fb3a9c9..66d39ea6bd10 100644
> > --- a/drivers/char/tpm/Makefile
> > +++ b/drivers/char/tpm/Makefile
> > @@ -27,6 +27,8 @@ obj-$(CONFIG_TCG_TIS_SPI) += tpm_tis_spi.o
> > tpm_tis_spi-y := tpm_tis_spi_main.o
> > tpm_tis_spi-$(CONFIG_TCG_TIS_SPI_CR50) += tpm_tis_spi_cr50.o
> >
> > +obj-$(CONFIG_TCG_TIS_I2C_CR50) += tpm_tis_i2c_cr50.o
> > +
> > obj-$(CONFIG_TCG_TIS_I2C_ATMEL) += tpm_i2c_atmel.o
> > obj-$(CONFIG_TCG_TIS_I2C_INFINEON) += tpm_i2c_infineon.o
> > obj-$(CONFIG_TCG_TIS_I2C_NUVOTON) += tpm_i2c_nuvoton.o
> > diff --git a/drivers/char/tpm/tpm_tis_i2c_cr50.c b/drivers/char/tpm/tpm_tis_i2c_cr50.c
> > new file mode 100644
> > index 000000000000..37555dafdca0
> > --- /dev/null
> > +++ b/drivers/char/tpm/tpm_tis_i2c_cr50.c
> > @@ -0,0 +1,768 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Copyright 2016 Google Inc.
> > + *
> > + * Based on Linux Kernel TPM driver by
> > + * Peter Huewe <peter.huewe@...ineon.com>
> > + * Copyright (C) 2011 Infineon Technologies
> > + */
> > +
> > +/*
> > + * cr50 is a firmware for H1 secure modules that requires special
> > + * handling for the I2C interface.
> > + *
> > + * - Use an interrupt for transaction status instead of hardcoded delays
> > + * - Must use write+wait+read read protocol
> > + * - All 4 bytes of status register must be read/written at once
> > + * - Burst count max is 63 bytes, and burst count behaves
> > + * slightly differently than other I2C TPMs
> > + * - When reading from FIFO the full burstcnt must be read
> > + * instead of just reading header and determining the remainder
> > + */
> > +
> > +#include <linux/acpi.h>
> > +#include <linux/completion.h>
> > +#include <linux/i2c.h>
> > +#include <linux/interrupt.h>
> > +#include <linux/module.h>
> > +#include <linux/pm.h>
> > +#include <linux/slab.h>
> > +#include <linux/wait.h>
> > +
> > +#include "tpm_tis_core.h"
> > +
> > +#define CR50_MAX_BUFSIZE 64
> > +#define CR50_TIMEOUT_SHORT_MS 2 /* Short timeout during transactions */
> > +#define CR50_TIMEOUT_NOIRQ_MS 20 /* Timeout for TPM ready without IRQ */
> > +#define CR50_I2C_DID_VID 0x00281ae0L
> > +#define CR50_I2C_MAX_RETRIES 3 /* Max retries due to I2C errors */
> > +#define CR50_I2C_RETRY_DELAY_LO 55 /* Min usecs between retries on I2C */
> > +#define CR50_I2C_RETRY_DELAY_HI 65 /* Max usecs between retries on I2C */
>
> CR50_ -> TPM_CR50_
>
> > +
> > +#define TPM_I2C_ACCESS(l) (0x0000 | ((l) << 4))
> > +#define TPM_I2C_STS(l) (0x0001 | ((l) << 4))
> > +#define TPM_I2C_DATA_FIFO(l) (0x0005 | ((l) << 4))
> > +#define TPM_I2C_DID_VID(l) (0x0006 | ((l) << 4))
> > +
> > +struct priv_data {
> > + int irq;
> > + int locality;
> > + struct completion tpm_ready;
> > + u8 buf[CR50_MAX_BUFSIZE];
> > +};
>
> tpm_i2c_cr50_priv_data
>
> > +
> > +enum force_release {
> > + CR50_NO_FORCE = 0x0,
> > + CR50_FORCE = 0x1,
> > +};
>
> I'd just
>
> #define TPM_I2C_CR50_NO_FORCE 0
> #define TPM_I2C_CR50_FORCE 1
>
A proper enumerated type has advantages over a preprocessor macro:
even if the compiler won't warn you, static analyzers can warn
about a misuse.
Also, it allows for a more obvious prototype.
I am curious why do you propose this change?
Thanks,
Ezequiel
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