linux-kernel - Re: [PATCH 2/2] tpm: add driver for cr50 on SPI

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Date:	Thu, 21 Jul 2016 11:10:47 -0700
From:	Andrey Pronin <apronin@...omium.org>
To:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc:	Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
	Peter Huewe <peterhuewe@....de>,
	Marcel Selhorst <tpmdd@...horst.net>,
	tpmdd-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
	groeck@...omium.org, smbarber@...omium.org, dianders@...omium.org,
	Christophe Ricard <christophe.ricard@...il.com>
Subject: Re: [PATCH 2/2] tpm: add driver for cr50 on SPI

On Wed, Jul 20, 2016 at 11:03:36AM -0600, Jason Gunthorpe wrote:
> On Tue, Jul 19, 2016 at 05:24:11PM -0700, Andrey Pronin wrote:
> 
> > The only two things that bother me with such approach are
> > (1) whatever names I pick for the new set of functions, they
> >     will be similar to and thus might be confused with the
> >     original tpm_tis_read/writeXX;
> 
> tpm_tis_helper_read16 ?
> 
> > (2) these functions are phy-specific, so possibly it's better
> >     to create tpm_tis_spi.h and put them there with proper
> >     name prefixes. And then use in tpm_tis_spi and cr50_spi.
> 
> No, they are generic to any tis phy that implements read only through
> read_bytes.
> 
> (Honestly, I'm not sure we made the best choice here having phy
>  functions for all the versions, we are not that performance
>  sensitive, just getting rid of everything but read_bytes from the
>  phy_ops would probably also be a reasonable thing to do.)
> 

One thing we can do is re-implement functions tpm_tis_read/writeXX
to use phy-specific implementations of read16, read32, write32 if they
are provided. But if those function pointers are left NULL in phy_ops,
fallback to using read/write_bytes and byte-swapping.

I.e., instead of:

static inline int tpm_tis_read16(struct tpm_tis_data *data, u32 addr,
				 u16 *result)
{
	return data->phy_ops->read16(data, addr, result);
}

do the following:

static inline int tpm_tis_read16(struct tpm_tis_data *data, u32 addr,
				 u16 *result)
{
        int rc;

	if (data->phy_ops->read16)
		return data->phy_ops->read16(data, addr, result);

	rc = data->phy_ops->read_bytes(data, addr,
				       sizeof(u16), (u8 *)result);
	if (!rc)
		*result = le16_to_cpu(*result);
	return rc;
}

If you like the idea, I'll submit it as a separate patch.

Andrey