Re: [PATCH 01/16] remoteproc: Extend rproc_da_to_va() API with a flags parameter

From: David Lechner <david@lechnology.com>
To: Roger Quadros <rogerq@ti.com>,
	ohad@wizery.com, bjorn.andersson@linaro.org, s-anna@ti.com
Cc: tony@atomide.com, robh+dt@kernel.org, bcousson@baylibre.com,
	ssantosh@kernel.org, nsekhar@ti.com, t-kristo@ti.com,
	nsaulnier@ti.com, jreeder@ti.com, m-karicheri2@ti.com,
	woods.technical@gmail.com, linux-omap@vger.kernel.org,
	linux-remoteproc@vger.kernel.org, linux-kernel@vger.kernel.org,
	devicetree@vger.kernel.org
Subject: Re: [PATCH 01/16] remoteproc: Extend rproc_da_to_va() API with a flags parameter
Date: Thu, 29 Nov 2018 10:12:42 -0600	[thread overview]
Message-ID: <ec83108c-1748-cec4-bebf-119d261fb229@lechnology.com> (raw)
In-Reply-To: <5BFFBFA0.9000104@ti.com>

On 11/29/18 4:29 AM, Roger Quadros wrote:
> Bjorn, Suman,
> 
> On 26/11/18 23:29, David Lechner wrote:
>> On 11/26/18 1:52 AM, Roger Quadros wrote:
>>> From: Suman Anna <s-anna@ti.com>
>>>
>>> The rproc_da_to_va() API is currently used to perform any device
>>> to kernel address translations to meet the different needs of the
>>> remoteproc core/platform drivers (eg: loading). The function also
>>> invokes the da_to_va ops, if present, to allow the remoteproc
>>> platform drivers to provide address translation. However, not all
>>> platform implementations have linear address spaces, and may need
>>> an additional parameter to be able to perform proper translations.
>>>
>>> The rproc_da_to_va() API and the rproc .da_to_va ops have therefore
>>> been expanded to take in an additional flags field enabling some
>>> remoteproc implementations (like the TI PRUSS remoteproc driver)
>>> to use these flags. Also, define some semantics for this flags
>>> argument as this can vary from one implementation to another. A
>>> new flags type is encoded into the upper 16 bits along side the
>>> actual value in the lower 16-bits for the flags argument, to
>>> allow different individual implementations to have better
>>> flexibility in interpreting the flags as per their needs.
>>
>> This seems like an overly complex solution for a rather simple
>> problem. Instead of passing all sorts of flags, could we just add
>> a parameter named "page" to da_to_va() that indicates the memory
>> page of the address in the remote processor?
>>
>> Or perhaps there is some other use for all of these flags that I
>> am not aware of?
> 
> I'm not a big fan of this patch either.
> 
> rproc_da_to_va() is used at the following places
> 
> 2 qcom_q6v5_mss.c         qcom_q6v5_dump_segment           974 void *ptr = rproc_da_to_va(rproc, segment->da, segment->size,
> 3 remoteproc_core.c       rproc_da_to_va                   197 void *rproc_da_to_va(struct rproc *rproc, u64 da, int len, u32 flags)
> 4 remoteproc_core.c       rproc_handle_trace               582 ptr = rproc_da_to_va(rproc, rsc->da, rsc->len, RPROC_FLAGS_NONE);
> 5 remoteproc_core.c       rproc_coredump                  1592 ptr = rproc_da_to_va(rproc, segment->da, segment->size,
> 6 remoteproc_elf_loader.c rproc_elf_load_segments          185 ptr = rproc_da_to_va(rproc, da, memsz,
> 7 remoteproc_elf_loader.c rproc_elf_find_loaded_rsc_table  337 return rproc_da_to_va(rproc, shdr->sh_addr, shdr->sh_size,
> 
> At rproc_elf_load_segments() we need to pass enough information so that
> the rproc driver can load the segment into proper area (IRAM vs DRAM).
> So providing page should suffice.

FYI, the PRU series I sent a while back has some patches to do
something like this so feel free to use them if they are helpful.

https://lore.kernel.org/lkml/20180623210810.21232-2-david@lechnology.com/
https://lore.kernel.org/lkml/20180623210810.21232-3-david@lechnology.com/

> 
> I want to understand more about rproc_elf_find_loaded_rsc_table() myself.
> rproc_elf_find_loaded_rsc_table() is called only in rproc_start() in remoteproc_core.c
> with the comment
> 
>          /*
>           * The starting device has been given the rproc->cached_table as the
>           * resource table. The address of the vring along with the other
>           * allocated resources (carveouts etc) is stored in cached_table.
>           * In order to pass this information to the remote device we must copy
>           * this information to device memory. We also update the table_ptr so
>           * that any subsequent changes will be applied to the loaded version.
>           */
>          loaded_table = rproc_find_loaded_rsc_table(rproc, fw);
> 
> Why isn't cached_table sufficient?
> Why do we need to call rproc_find_loaded_rsc_table()?
> 
> why do we need to load the resource table into remote processor memory at all.
> As discussed earlier, some PRU systems have very little memory (512 bytes?)
> and we want to avoid unnecessary loading.
> 
> cheers,
> -roger
> 