linux-kernel - Re: [PATCH v6 1/4] firmware: scm: Add new SCM call API for switching memory ownership

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Message-ID: <20170712191914.GI1618@tuxbook>
Date:   Wed, 12 Jul 2017 12:19:14 -0700
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     "Dwivedi, Avaneesh Kumar (avani)" <akdwived@...eaurora.org>
Cc:     Stephen Boyd <sboyd@...eaurora.org>, agross@...eaurora.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-remoteproc@...r.kernel.org
Subject: Re: [PATCH v6 1/4] firmware: scm: Add new SCM call API for switching
 memory ownership

On Wed 12 Jul 04:03 PDT 2017, Dwivedi, Avaneesh Kumar (avani) wrote:

> 
> 
> On 7/8/2017 4:19 AM, Stephen Boyd wrote:
> > On 06/22, Avaneesh Kumar Dwivedi wrote:
> > > diff --git a/drivers/firmware/qcom_scm-64.c b/drivers/firmware/qcom_scm-64.c
> > > index 6e6d561..cdfe986 100644
> > > --- a/drivers/firmware/qcom_scm-64.c
> > > +++ b/drivers/firmware/qcom_scm-64.c
> > > @@ -292,6 +304,86 @@ int qcom_scm_pas_shutdown(u32 peripheral)
> > >   }
> > >   EXPORT_SYMBOL(qcom_scm_pas_shutdown);
> > > +/**
> > > + * qcom_scm_assign_mem() - Make a secure call to reassign memory ownership
> > > + *
> > > + * @mem_addr: mem region whose ownership need to be reassigned
> > > + * @mem_sz:   size of the region.
> > > + * @srcvm:    vmid for current set of owners, each set bit in
> > > + *            flag indicate a unique owner
> > > + * @newvm:    array having new owners and corrsponding permission
> > > + *            flags
> > > + * @dest_cnt: number of owners in next set.
> > > + * Return next set of owners on success.
> > > + */
> > > +int qcom_scm_assign_mem(phys_addr_t mem_addr, size_t mem_sz, int srcvm,
> > > +			struct qcom_scm_vmperm *newvm, int dest_cnt)
> > > +{
> > > +	unsigned long dma_attrs = DMA_ATTR_FORCE_CONTIGUOUS;
> > Why do we need this? Just curious if we can drop this.
> The force contiguous flag is required with dma_alloc_attrs() api to allocate
> memory from physically contiguous zone.
> I am not sure, are you saying that api will work without the attribute or
> you mean i shall use some api which does not take explicit attribute?
> > 
> > > +	struct qcom_scm_current_perm_info *destvm;
> > > +	struct qcom_scm_mem_map_info *mem;
> > > +	phys_addr_t memory_phys;
> > > +	phys_addr_t dest_phys;
> > > +	phys_addr_t src_phys;
> > > +	size_t mem_all_sz;
> > > +	size_t memory_sz;
> > > +	size_t dest_sz;
> > > +	size_t src_sz;
> > > +	int next_vm;
> > > +	__le32 *src;
> > > +	void *ptr;
> > > +	int ret;
> > > +	int len;
> > > +	int i;
> > > +
> > > +	src_sz = hweight_long(srcvm) * sizeof(*src);
> > > +	memory_sz = sizeof(*mem);
> > > +	dest_sz = dest_cnt*sizeof(*destvm);
> > > +	mem_all_sz = src_sz + memory_sz + dest_sz;
> > > +
> > > +	ptr = dma_alloc_attrs(__scm->dev, ALIGN(mem_all_sz, SZ_64),
> > > +		&src_phys, GFP_KERNEL, dma_attrs);
> > > +	if (!ptr)
> > > +		return -ENOMEM;
> > > +
> > > +	/* Fill source vmid detail */
> > > +	src = (__le32 *)ptr;
> > Cast is necessary?
> i removed many type casting but few still lingering, will check and remove
> whatever unnecessary.
> > 
> > > +	len = hweight_long(srcvm);
> > > +	for (i = 0; i < len; i++) {
> > > +		src[i] = cpu_to_le32(ffs(srcvm) - 1);
> > > +		srcvm ^= 1 << (ffs(srcvm) - 1);
> > > +	}
> > > +
> > > +	/* Fill details of mem buff to map */
> > > +	mem = ptr + ALIGN(src_sz, SZ_64);
> > > +	memory_phys = src_phys + ALIGN(src_sz, SZ_64);
> > > +	mem[0].mem_addr = cpu_to_le64(mem_addr);
> > > +	mem[0].mem_size = cpu_to_le64(mem_sz);
> > > +
> > > +	next_vm = 0;
> > > +	/* Fill details of next vmid detail */
> > > +	destvm = ptr + ALIGN(memory_sz, SZ_64) + ALIGN(src_sz, SZ_64);
> > > +	dest_phys = memory_phys + ALIGN(memory_sz, SZ_64);
> > > +	for (i = 0; i < dest_cnt; i++) {
> > > +		destvm[i].vmid = cpu_to_le32(newvm[i].vmid);
> > > +		destvm[i].perm = cpu_to_le32(newvm[i].perm);
> > > +		destvm[i].ctx = 0;
> > > +		destvm[i].ctx_size = 0;
> > > +		next_vm |= BIT(newvm[i].vmid);
> > > +	}
> > > +
> > > +	ret = __qcom_scm_assign_mem(__scm->dev, memory_phys,
> > > +		memory_sz, src_phys, src_sz, dest_phys, dest_sz);
> > > +	dma_free_attrs(__scm->dev, ALIGN(mem_all_sz, SZ_64),
> > > +		ptr, src_phys, dma_attrs);
> > > +	if (ret == 0)
> > > +		return next_vm;
> > > +	else if (ret > 0)
> > > +		return -ret;
> > This still confuses me. Do we really just pass whatever the
> > firmware tells us the error code is up to the caller? Shouldn't
> > we be remapping the scm errors we receive to normal linux errnos?
> because i do not know in advance what exactly will be the return error code,
> moreover there are number of error codes which are returned in case of
> failure
> so if i have to return linux error code, i can not do one to one mapping of
> error code and will have to return single error code for all failure.
> let me know your comments further on this.+ return ret;

Returning a single error code for all these cases (e.g. -EINVAL) is
fine.


You could amend this by translating some of the results to other codes,
if that makes sense. But I'm not aware of the kind of errors this
interface can return, so it's hard to advice on this.

Regards,
Bjorn