linux-kernel - Re: [PATCH v11 3/4] tee: add OP-TEE driver

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Message-ID: <20160901092213.GA3968@ermac>
Date:   Thu, 1 Sep 2016 11:22:18 +0200
From:   Jens Wiklander <jens.wiklander@...aro.org>
To:     "Andrew F. Davis" <afd@...com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        devicetree@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Al Viro <viro@...IV.linux.org.uk>, valentin.manea@...wei.com,
        jean-michel.delorme@...com, emmanuel.michel@...com,
        javier@...igon.com,
        Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
        Mark Rutland <mark.rutland@....com>,
        Michal Simek <michal.simek@...inx.com>,
        Rob Herring <robh+dt@...nel.org>,
        Will Deacon <will.deacon@....com>,
        Arnd Bergmann <arnd@...db.de>, Nishanth Menon <nm@...com>
Subject: Re: [PATCH v11 3/4] tee: add OP-TEE driver

On Wed, Aug 31, 2016 at 11:40:20AM -0500, Andrew F. Davis wrote:
> On 08/31/2016 08:50 AM, Jens Wiklander wrote:
> > On Tue, Aug 30, 2016 at 03:23:24PM -0500, Andrew F. Davis wrote:
> >> On 08/22/2016 08:00 AM, Jens Wiklander wrote:
> >>> +static struct tee_shm_pool *
> >>> +optee_config_shm_ioremap(struct device *dev, optee_invoke_fn *invoke_fn,
> >>> +			 void __iomem **ioremaped_shm)
> >>> +{
> >>> +	struct arm_smccc_res res;
> >>> +	struct tee_shm_pool *pool;
> >>> +	unsigned long vaddr;
> >>> +	phys_addr_t paddr;
> >>> +	size_t size;
> >>> +	phys_addr_t begin;
> >>> +	phys_addr_t end;
> >>> +	void __iomem *va;
> >>> +	struct tee_shm_pool_mem_info priv_info;
> >>> +	struct tee_shm_pool_mem_info dmabuf_info;
> >>> +
> >>> +	invoke_fn(OPTEE_SMC_GET_SHM_CONFIG, 0, 0, 0, 0, 0, 0, 0, &res);
> >>> +	if (res.a0 != OPTEE_SMC_RETURN_OK) {
> >>> +		dev_info(dev, "shm service not available\n");
> >>> +		return ERR_PTR(-ENOENT);
> >>> +	}
> >>> +
> >>> +	if (res.a3 != OPTEE_SMC_SHM_CACHED) {
> >>> +		dev_err(dev, "only normal cached shared memory supported\n");
> >>> +		return ERR_PTR(-EINVAL);
> >>> +	}
> >>> +
> >>> +	begin = roundup(res.a1, PAGE_SIZE);
> >>> +	end = rounddown(res.a1 + res.a2, PAGE_SIZE);
> >>
> >> res.a1/2/3 is really hard to review and understand, would it work better
> >> to use a union or cast for the output of invoke_fn based on the function
> >> type?
> >>
> >> In the header that defines what the returned info from these calls means
> >> add:
> >>
> >> struct OPTEE_SMC_GET_SHM_CONFIG_RESULT {
> >> 	unsigned long status;
> >> 	unsigned long start;
> >> 	unsigned long size;
> >> 	unsigned long settings;
> >> };
> >>
> >> then:
> >>
> >> union something result;
> >>
> >> begin = roundup(result.ret.start, PAGE_SIZE);
> >> end = rounddown(result.ret.start + result.ret.size, PAGE_SIZE);
> >>
> >> or similar with just casting to the better named struct type.
> > 
> > optee_smc.h describes what's passed in the registers during an SMC I'd
> > rather not clutter it with structs that doesn't add any information
> > there. I'm not that happy with casting or using unions to alias struct
> > arm_smccc_res either. How about a simple wrapper function for this call
> > to deal with the details instead?
> > 
> 
> I think that would be a good idea anyway, for instance, someday if the
> interface changes slightly then you will be able to contain the
> compatibility fixes in the wrapper and not out here in the main driver.

That interface is supposed to be a stable ABI, incompatible changes in
the ABI should be discouraged. If there's an incompatible change it has
to be dealt with in the main driver. A small wrapper function in a
standalone header file has no chance here as it probably involves using
information gathered while probing secure world.

What I meant was a small wrapper function just above 
optee_config_shm_ioremap() to deal with only this call.

> >> [snip]
> >>
> >>> +#define OPTEE_MSG_ATTR_CACHE_SHIFT		16
> >>> +#define OPTEE_MSG_ATTR_CACHE_MASK		0x7
> >>
> >> GENMASK
> > 
> > Do you mean that OPTEE_MSG_ATTR_CACHE_MASK should be defined using the
> > GENMASK() macro? If so I guess I should update OPTEE_MSG_ATTR_TYPE_MASK
> > also.
> > 
> 
> Right, I can tell what bits 0x7 mask, but sometimes it's not so easy
> (7F8, etc) so I find it's best to use GENMASKS for all masks so I don't
> have to ever think about it at all.
> 
> Also I like to mask then shift, so it would be:
> 
> #define OPTEE_MSG_ATTR_CACHE_SHIFT	16
> #define OPTEE_MSG_ATTR_CACHE_MASK	GENMASK(18, 16)
> 
> Then we can see at a glance the actual bits we are looking for (18-16)
> and verify the shift is the right amount.

I'm wired the other way around, I usually shift then mask, I suppose
it's a matter of taste. I'm happy to use GENMASK instead to define
OPTEE_MSG_ATTR_CACHE_MASK, but I'd like to keep it unshifted if you
don't mind.

Thanks,
Jens