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    SubjectRe: [PATCH v6 4/4] tpm: tpm_tis_spi: Support cr50 devices
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    On Thu, 2019-08-29 at 15:41 -0700, Stephen Boyd wrote:
    > From: Andrey Pronin <apronin@chromium.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
    >
    > Cr50 firmware has a requirement to wait for the TPM to wakeup before
    > sending commands over the SPI bus. Otherwise, the firmware could be in
    > deep sleep and not respond. The method to wait for the device to wakeup
    > is slightly different than the usual flow control mechanism described in
    > the TCG SPI spec. Add a completion to tpm_tis_spi_transfer() before we
    > start a SPI transfer so we can keep track of the last time the TPM
    > driver accessed the SPI bus to support the flow control mechanism.
    >
    > Split the cr50 logic off into a different file to keep it out of the
    > normal code flow of the existing SPI driver while making it all part of
    > the same module when the code is optionally compiled into the same
    > module. Export a new function, tpm_tis_spi_init(), and the associated
    > read/write/transfer APIs so that we can do this. Make the cr50 code wrap
    > the tpm_tis_spi_phy struct with its own struct to override the behavior
    > of tpm_tis_spi_transfer() by supplying a custom flow control hook. This
    > shares the most code between the core driver and the cr50 support
    > without combining everything into the core driver or exporting module
    > symbols.
    >
    > Signed-off-by: Andrey Pronin <apronin@chromium.org>
    > Cc: Andrey Pronin <apronin@chromium.org>
    > Cc: Duncan Laurie <dlaurie@chromium.org>
    > Cc: Jason Gunthorpe <jgg@ziepe.ca>
    > Cc: Arnd Bergmann <arnd@arndb.de>
    > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    > Cc: Guenter Roeck <groeck@chromium.org>
    > Cc: Alexander Steffen <Alexander.Steffen@infineon.com>
    > Cc: Heiko Stuebner <heiko@sntech.de>

    Had to time to look at this patch set after all before LPC. I just
    realized that the kconfig has taken away. Not sure why is that
    because there's been only request to not have a new LKM. There
    still should be ability opt-out to have Cr50 support in vmlinux.

    /Jarkko

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