linux-kernel - Re: [PATCH RFC 1/2] tpm: tpm_tis

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Message-ID: <e7d402f4-0463-4bb2-b1ea-afb36a58e59a@gmx.net>
Date: Fri, 6 Sep 2024 16:46:52 +0200
From: Stefan Wahren <wahrenst@....net>
To: Jarkko Sakkinen <jarkko@...nel.org>, Peter Huewe <peterhuewe@....de>,
 Jason Gunthorpe <jgg@...pe.ca>
Cc: linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org,
 Stefan Berger <stefanb@...ux.ibm.com>
Subject: Re: [PATCH RFC 1/2] tpm: tpm_tis_spi: Ensure SPI mode 0

Am 06.09.24 um 11:47 schrieb Jarkko Sakkinen:
> On Fri Sep 6, 2024 at 9:09 AM EEST, Stefan Wahren wrote:
>> According to TCG PC Client Platform TPM Profile (PTP) Specification
>> only SPI mode 0 is supported. In order to ensure the SPI controller
>> supports the necessary settings, call spi_setup() and bail out
>> as soon as possible in error case.
>>
>> This change should affect all supported TPM SPI devices, because
>> tpm_tis_spi_probe is either called direct or indirectly.
>>
>> Signed-off-by: Stefan Wahren <wahrenst@....net>
>> ---
>>   drivers/char/tpm/tpm_tis_spi_main.c | 11 +++++++++++
>>   1 file changed, 11 insertions(+)
>>
>> diff --git a/drivers/char/tpm/tpm_tis_spi_main.c b/drivers/char/tpm/tpm_tis_spi_main.c
>> index 61b42c83ced8..e62d297b040e 100644
>> --- a/drivers/char/tpm/tpm_tis_spi_main.c
>> +++ b/drivers/char/tpm/tpm_tis_spi_main.c
>> @@ -248,6 +248,17 @@ static int tpm_tis_spi_write_bytes(struct tpm_tis_data *data, u32 addr,
>>   int tpm_tis_spi_init(struct spi_device *spi, struct tpm_tis_spi_phy *phy,
>>   		     int irq, const struct tpm_tis_phy_ops *phy_ops)
>>   {
>> +	int ret;
>> +
>> +	spi->mode &= ~SPI_MODE_X_MASK;
>> +	spi->mode |= SPI_MODE_0;
>> +
>> +	ret = spi_setup(spi);
>> +	if (ret < 0) {
>> +		dev_err(&spi->dev, "SPI setup failed: %d\n", ret);
>> +		return ret;
>> +	}
>> +
>>   	phy->iobuf = devm_kmalloc(&spi->dev, SPI_HDRSIZE + MAX_SPI_FRAMESIZE, GFP_KERNEL);
>>   	if (!phy->iobuf)
>>   		return -ENOMEM;
>> --
>> 2.34.1
>
> Why?
SPI protocol driver usually call spi_setup to verify that the SPI
controller accept the settings (SPI mode, bit, clock rate ...). Bailing
out early is more helpful for debugging issues.
>
> BR, Jarkko