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[PATCH 4.9 015/164] tpm_tis_spi: Add small delay after last transfer

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4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Peter Huewe <peter.huewe@infineon.com>

commit 5cc0101d1f88500f8901d01b035af743215d4c3a upstream.

Testing the implementation with a Raspberry Pi 2 showed that under some
circumstances its SPI master erroneously releases the CS line before the
transfer is complete, i.e. before the end of the last clock. In this case
the TPM ignores the transfer and misses for example the GO command. The
driver is unable to detect this communication problem and will wait for a
command response that is never going to arrive, timing out eventually.

As a workaround, the small delay ensures that the CS line is held long
enough, even with a faulty SPI master. Other SPI masters are not affected,
except for a negligible performance penalty.

Fixes: 0edbfea537d1 ("tpm/tpm_tis_spi: Add support for spi phy")
Signed-off-by: Alexander Steffen <Alexander.Steffen@infineon.com>
Signed-off-by: Peter Huewe <peter.huewe@infineon.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Tested-by: Benoit Houyere <benoit.houyere@st.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/char/tpm/tpm_tis_spi.c |    1 +
 1 file changed, 1 insertion(+)

--- a/drivers/char/tpm/tpm_tis_spi.c
+++ b/drivers/char/tpm/tpm_tis_spi.c
@@ -112,6 +112,7 @@ static int tpm_tis_spi_transfer(struct t
 
 		spi_xfer.cs_change = 0;
 		spi_xfer.len = transfer_len;
+		spi_xfer.delay_usecs = 5;
 
 		if (direction) {
 			spi_xfer.tx_buf = NULL;

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[PATCH 4.9 000/164] 4.9.30-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-24 00:00 +0200
  [PATCH 4.9 003/164] USB: ene_usb6250: fix DMA to the stack Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-24 00:00 +0200
  [PATCH 4.9 030/164] dm space map disk: fix some book keeping in the disk space map Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-24 00:00 +0200
  [PATCH 4.9 051/164] drm/nouveau/tmr: ack interrupt before processing alarms Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-24 00:00 +0200
  [PATCH 4.9 029/164] dm thin metadata: call precommit before saving the roots Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-24 00:00 +0200
  [PATCH 4.9 015/164] tpm_tis_spi: Add small delay after last transfer Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-24 00:00 +0200
  [PATCH 4.9 023/164] dm raid: select the Kconfig option CONFIG_MD_RAID0 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-24 00:00 +0200
  [PATCH 4.9 006/164] USB: core: replace %p with %pK Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-24 00:00 +0200
  Re: [PATCH 4.9 000/164] 4.9.30-stable review Guenter Roeck <linux@roeck-us.net> - 2017-05-24 06:00 +0200
    Re: [PATCH 4.9 000/164] 4.9.30-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-24 09:10 +0200
    Re: [PATCH 4.9 000/164] 4.9.30-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-24 09:20 +0200
  Re: [PATCH 4.9 000/164] 4.9.30-stable review Guenter Roeck <linux@roeck-us.net> - 2017-05-24 22:30 +0200

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