linux-kernel - Re: [PATCH 4/5] tpm_tis_spi: Remove limitation of transfers to MAX_SPI

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Date:   Fri, 24 Feb 2017 13:55:52 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Peter Huewe <peter.huewe@...ineon.com>
Cc:     Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
        tpmdd-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
        peterhuewe@....de, Christophe Ricard <christophe-h.ricard@...com>,
        stable@...r.kernel.org,
        Alexander Steffen <Alexander.Steffen@...ineon.com>
Subject: Re: [PATCH 4/5] tpm_tis_spi: Remove limitation of transfers to
 MAX_SPI_FRAMESIZE bytes

On Thu, Feb 16, 2017 at 04:08:25PM +0000, Peter Huewe wrote:
> Limiting transfers to MAX_SPI_FRAMESIZE was not expected by the upper
> layers, as tpm_tis has no such limitation. Add a loop to hide that
> limitation.
> 
> Cc: <stable@...r.kernel.org>
> Fixes: 0edbfea537d1 ("tpm/tpm_tis_spi: Add support for spi phy")
> Signed-off-by: Alexander Steffen <Alexander.Steffen@...ineon.com>
> Signed-off-by: Peter Huewe <peter.huewe@...ineon.com>
> ---
>  drivers/char/tpm/tpm_tis_spi.c | 108 ++++++++++++++++++++++-------------------
>  1 file changed, 57 insertions(+), 51 deletions(-)
> 
> diff --git a/drivers/char/tpm/tpm_tis_spi.c b/drivers/char/tpm/tpm_tis_spi.c
> index 16938e2253d2..b50c5b072df3 100644
> --- a/drivers/char/tpm/tpm_tis_spi.c
> +++ b/drivers/char/tpm/tpm_tis_spi.c
> @@ -61,68 +61,74 @@ static int tpm_tis_spi_transfer(struct tpm_tis_data *data, u32 addr, u8 len,
>  {
>  	struct tpm_tis_spi_phy *phy = to_tpm_tis_spi_phy(data);
>  	int ret;
> -	struct spi_message m;
> -	struct spi_transfer spi_xfer = {
> -		.tx_buf = phy->tx_buf,
> -		.rx_buf = phy->rx_buf,
> -		.len = 4,
> -		.cs_change = 1,
> -	};
> -
> -	if (len > MAX_SPI_FRAMESIZE)
> -		return -ENOMEM;
>  
> -	phy->tx_buf[0] = direction | (len - 1);
> -	phy->tx_buf[1] = 0xd4;
> -	phy->tx_buf[2] = addr >> 8;
> -	phy->tx_buf[3] = addr;
> +	spi_bus_lock(phy->spi_device->master);
>  
> -	spi_message_init(&m);
> -	spi_message_add_tail(&spi_xfer, &m);
> +	while (len) {
> +		struct spi_message m;
> +		struct spi_transfer spi_xfer = {
> +			.tx_buf = phy->tx_buf,
> +			.rx_buf = phy->rx_buf,
> +			.len = 4,
> +			.cs_change = 1,
> +		};

I like the habbit of keeping all the declarations in the beginning of
the function as we mostly have in the subsystem. It gives a fast view
what the function eats and how much stack it uses.

If you really think that declaring spi_xfer here is a good idea please
create a separate "helper" function for it.

/Jarkko