From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jon Hunter Subject: Re: [PATCH] [RFC] dmaengine: add fifo_size member Date: Fri, 7 Jun 2019 10:24:00 +0100 Message-ID: References: <1556623828-21577-1-git-send-email-spujar@nvidia.com> <3368d1e1-0d7f-f602-5b96-a978fcf4d91b@nvidia.com> <20190504102304.GZ3845@vkoul-mobl.Dlink> <20190506155046.GH3845@vkoul-mobl.Dlink> <4cab47d0-41c3-5a87-48e1-d7f085c2e091@nvidia.com> <8a5b84db-c00b-fff4-543f-69d90c245660@nvidia.com> <3f836a10-eaf3-f59b-7170-6fe937cf2e43@ti.com> <4593f37c-5e89-8559-4e80-99dbfe4235de@nvidia.com> <50e1f9ed-1ea0-38f6-1a77-febd6a3a0848@gmail.com> <4b098fb6-1a5b-1100-ae16-978a887c9535@nvidia.com> <457eb5e1-40cc-8c0f-e21c-3881c3c04de2@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <457eb5e1-40cc-8c0f-e21c-3881c3c04de2@gmail.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Dmitry Osipenko , Peter Ujfalusi , Sameer Pujar , Vinod Koul Cc: dan.j.williams@intel.com, tiwai@suse.com, dmaengine@vger.kernel.org, linux-kernel@vger.kernel.org, sharadg@nvidia.com, rlokhande@nvidia.com, dramesh@nvidia.com, mkumard@nvidia.com, linux-tegra List-Id: linux-tegra@vger.kernel.org On 06/06/2019 18:25, Dmitry Osipenko wrote: > 06.06.2019 19:53, Jon Hunter =D0=BF=D0=B8=D1=88=D0=B5=D1=82: >> >> On 06/06/2019 17:44, Dmitry Osipenko wrote: >>> 06.06.2019 19:32, Jon Hunter =D0=BF=D0=B8=D1=88=D0=B5=D1=82: >>>> >>>> On 06/06/2019 16:18, Dmitry Osipenko wrote: >>>> >>>> ... >>>> >>>>>>> If I understood everything correctly, the FIFO buffer is shared amo= ng >>>>>>> all of the ADMA clients and hence it should be up to the ADMA drive= r to >>>>>>> manage the quotas of the clients. So if there is only one client th= at >>>>>>> uses ADMA at a time, then this client will get a whole FIFO buffer,= but >>>>>>> once another client starts to use ADMA, then the ADMA driver will h= ave >>>>>>> to reconfigure hardware to split the quotas. >>>>>> >>>>>> The FIFO quotas are managed by the ADMAIF driver (does not exist in >>>>>> mainline currently but we are working to upstream this) because it i= s >>>>>> this device that owns and needs to configure the FIFOs. So it is rea= lly >>>>>> a means to pass the information from the ADMAIF to the ADMA. >>>>> >>>>> So you'd want to reserve a larger FIFO for an audio channel that has = a >>>>> higher audio rate since it will perform reads more often. You could a= lso >>>>> prioritize one channel over the others, like in a case of audio call = for >>>>> example. >>>>> >>>>> Is the shared buffer smaller than may be needed by clients in a worst >>>>> case scenario? If you could split the quotas statically such that eac= h >>>>> client won't ever starve, then seems there is no much need in the >>>>> dynamic configuration. >>>> >>>> Actually, this is still very much relevant for the static case. Even i= f >>>> we defined a static configuration of the FIFO mapping in the ADMAIF >>>> driver we still need to pass this information to the ADMA. I don't >>>> really like the idea of having it statically defined in two different >>>> drivers. >>> >>> Ah, so you need to apply the same configuration in two places. Correct? >>> >>> Are ADMAIF and ADMA really two different hardware blocks? Or you >>> artificially decoupled the ADMA driver? >> >> These are two different hardware modules with their own register sets. >> Yes otherwise, it would be a lot simpler! >=20 > The register sets are indeed separated, but it looks like that ADMAIF is > really a part of ADMA that is facing to Audio Crossbar. No? What is the > purpose of ADMAIF? Maybe you could amend the ADMA hardware description > with the ADMAIF addition until it's too late. The ADMA can perform the following transfers (per the CH_CONFIG register) ... MEMORY_TO_MEMORY AHUB_TO_MEMORY MEMORY_TO_AHUB AHUB_TO_AHUB Hence it is possible to use the ADMA to do memory-to-memory transfers that do not involve the ADMAIF. So no the ADMAIF is not part of the ADMA. It is purely the interface to the crossbar (AHUB/APE), but from a hardware standpoint they are separate. And so no we will not amend the hardware description. Jon --=20 nvpublic