linux-kernel - Re: [PATCH v2] dt-bindings: media: Add sram-size Property for Wave5

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Message-ID: <49067f872e56d6f315a8b1b93bea92e54cba4874.camel@ndufresne.ca>
Date: Fri, 09 Feb 2024 12:22:02 -0500
From: Nicolas Dufresne <nicolas@...fresne.ca>
To: Nishanth Menon <nm@...com>, Krzysztof Kozlowski
	 <krzysztof.kozlowski@...aro.org>
Cc: Brandon Brnich <b-brnich@...com>, Nas Chung <nas.chung@...psnmedia.com>,
  Jackson Lee <jackson.lee@...psnmedia.com>, Mauro Carvalho Chehab
 <mchehab@...nel.org>, Rob Herring <robh+dt@...nel.org>, Krzysztof Kozlowski
 <krzysztof.kozlowski+dt@...aro.org>,  Conor Dooley <conor+dt@...nel.org>,
 linux-media@...r.kernel.org, devicetree@...r.kernel.org, 
 linux-kernel@...r.kernel.org, Vignesh Raghavendra <vigneshr@...com>, Darren
 Etheridge <detheridge@...com>
Subject: Re: [PATCH v2] dt-bindings: media: Add sram-size Property for Wave5

Le vendredi 02 février 2024 à 06:52 -0600, Nishanth Menon a écrit :
> On 11:47-20240202, Krzysztof Kozlowski wrote:
> > On 01/02/2024 19:42, Brandon Brnich wrote:
> > > Wave521c has capability to use SRAM carveout to store reference data with
> > > purpose of reducing memory bandwidth. To properly use this pool, the driver
> > > expects to have an sram and sram-size node. Without sram-size node, driver
> > > will default value to zero, making sram node irrelevant.
> > 
> > I am sorry, but what driver expects should not be rationale for new
> > property. This justification suggests clearly it is not a property for DT.
> > 
> 
> Yup, the argumentation in the commit message is from the wrong
> perspective. bindings are OS agnostic hardware description, and what
> driver does with the description is driver's problem.
> 
> I will at least paraphrase my understanding:
> In this case, however, the hardware block will limp along with
> the usage of DDR (as is the current description), due to the
> latencies involved for DDR accesses. However, the hardware block
> has capability to use a substantially lower latency SRAM to provide
> proper performance and hence for example, deal with higher resolution

nit: I'd suggest to refer to "higher bandwidth" to generalize the combination
formed by resolution and frame rate. The resolution is always fixed with this
IP, regardless if its fast enough of not. It may not match the stream creator
intended frame rate though, which such optimization may fix.

> data streams. This SRAM is instantiated at SoC level rather than
> embedded within the hardware block itself.
> 
>