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

From: Dwivedi, Avaneesh Kumar (avani)
Date: Thu Jul 13 2017 - 03:33:46 EST

On 7/13/2017 11:24 AM, Stephen Boyd wrote:
On 07/12, 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)
+ * 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?
Does physically contiguous zone mean some CMA carveout? I wasn't
aware of a carveout for scm devices. I'm still not following the
reasoning here.
the memory will be allocated from common carveout, there is no scm device specific
carveout. i will use dma_alloc_coherent() and will drop off this flag.

we need physical contigious zone to fill and pass scm call parameters to TZ.

I'm saying that I don't understand why we need this flag. It
feels like this sort of constraint would apply all over the scm
driver if it was true, hence the confusion.

+ 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;
Yes, returning -EINVAL all the time is fine if we can't remap the
error. In fact, we should probably do what we do downstream and
print out the error value returned from the firmware to the
kernel log and then return some sane errno up to the caller. That
way the few people who know what the error codes mean can tell us
why the scm call failed.
OK, will do same.
just last thing to ask, should i resend all 4 patches together again or only one patch in v7 version.
as chnage will be in only 1 out of 4 patches.

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