Re: [PATCH v3 0/4] Improve VCHIQ cache line size handling

[Phil Elwell <phil@raspberrypi.org>]

On 17/09/2018 18:51, Florian Fainelli wrote:
> On 09/17/2018 04:47 AM, Phil Elwell wrote:
>> Hi Stefan,
>>
>> On 17/09/2018 12:39, Stefan Wahren wrote:
>>> Hi Phil,
>>>
>>> Am 17.09.2018 um 10:22 schrieb Phil Elwell:
>>>> Both sides of the VCHIQ communications mechanism need to agree on the cache
>>>> line size. Using an incorrect value can lead to data corruption, but having the
>>>> two sides using different values is usually worse.
>>>>
>>>> In the absence of an obvious convenient run-time method to determine the
>>>> correct value in the ARCH=arm world, the downstream Raspberry Pi trees used a
>>>> Device Tree property, written by the firmware, to configure the kernel driver.
>>>> This method was vetoed during the upstreaming process, so a fixed value of 32
>>>> was used instead, and some corruptions ensued. This is take 2 at arriving at
>>>> the correct value.
>>>>
>>>> Add a new compatible string - "brcm,bcm2836-vchiq" - to indicate an SoC with
>>>> a 64-byte cache line. Document the new string in the binding, and use it on
>>>> the appropriate platforms.
>>>>
>>>> The final patch is a (seemingly cosmetic) correction of the Device Tree "reg"
>>>> declaration for the device node, but it doubles as an indication to the
>>>> Raspberry Pi firmware that the kernel driver is running a recent kernel driver
>>>> that chooses the correct value. As such it would help if the DT patches are
>>>> not merged before the driver patch.
>>>>
>>>> v3: Builds without errors, tested on multiple Raspberry Pi models.
>>>> v2: Replaced ARM-specific logic used to determine cache line size with
>>>>      a new compatible string for BCM2836 and BCM2837.
>>>>
>>>> Phil Elwell (4):
>>>>    staging/vc04_services: Use correct cache line size
>>>>    dt-bindings: soc: Document "brcm,bcm2836-vchiq"
>>>>    ARM: dts: bcm283x: Correct vchiq compatible string
>>>>    ARM: dts: bcm283x: Correct mailbox register sizes
>>>
>>> since my pull requests are out, would it be okay to apply patch #1 for
>>> 4.20 and the DT stuff for 4.21 (with the assumption Rob is okay with
>>> these patches)?
>>
>> Patch 4 is the only one I'd like to be delayed, but delaying 2-4 is fine with me.
> 
> Humm, did you mean you would like not to be delayed? In any case Stefan,
> you can send an additional pull request, and I will merge it and send a
> second pull request towards ARM SoC maintainers, that's not a problem.

No, I meant what I wrote - I would prefer patch 1 to be merged before patch 4 (or at least
in the same release) to avoid the need for another firmware change, hence delaying patch
4 is good. It makes sense for the other commits to be merged in that order, but the
normal compatible-string fallback mechanism means there is no hard dependency there.

Phil