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

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Message-ID: <ef046a1b-4b13-9416-9f28-15f069cc80a8@codeaurora.org>
Date:   Thu, 13 Jul 2017 13:03:12 +0530
From:   "Dwivedi, Avaneesh Kumar (avani)" <akdwived@...eaurora.org>
To:     Stephen Boyd <sboyd@...eaurora.org>
Cc:     bjorn.andersson@...aro.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 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)
>>>>   }
>>>>   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?
> 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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