linux-kernel - Re: [PATCH v3 2/2] misc: sram: Add DMA-BUF Heap exporting of SRAM areas

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Date: Fri, 19 Apr 2024 18:57:47 +0200
From: Christian Gmeiner <christian.gmeiner@...il.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Pascal FONTAIN <Pascal.FONTAIN@...hmann.info>, linux-kernel@...r.kernel.org, 
	Derek Kiernan <derek.kiernan@....com>, Dragan Cvetic <dragan.cvetic@....com>, 
	Arnd Bergmann <arnd@...db.de>, Sumit Semwal <sumit.semwal@...aro.org>, 
	Christian König <christian.koenig@....com>, afd@...com, 
	linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org, 
	linaro-mm-sig@...ts.linaro.org
Subject: Re: [PATCH v3 2/2] misc: sram: Add DMA-BUF Heap exporting of SRAM areas

Am Di., 9. Apr. 2024 um 14:14 Uhr schrieb Greg Kroah-Hartman
<gregkh@...uxfoundation.org>:
>
> On Tue, Apr 09, 2024 at 02:06:05PM +0200, Pascal FONTAIN wrote:
> > From: Andrew Davis <afd@...com>
> >
> > This new export type exposes to userspace the SRAM area as a DMA-BUF
> > Heap,
> > this allows for allocations of DMA-BUFs that can be consumed by various
> > DMA-BUF supporting devices.
> >
> > Signed-off-by: Andrew Davis <afd@...com>
> > Tested-by: Pascal Fontain <pascal.fontain@...hmann.info>
>
> When sending on a patch from someone else, you too must sign off on it
> as per our documenation.  Please read it and understand what you are
> agreeing to when you do that for a new version please.
>
> > ---
> >  drivers/misc/Kconfig         |   7 +
> >  drivers/misc/Makefile        |   1 +
> >  drivers/misc/sram-dma-heap.c | 246 +++++++++++++++++++++++++++++++++++
> >  drivers/misc/sram.c          |   6 +
> >  drivers/misc/sram.h          |  16 +++
> >  5 files changed, 276 insertions(+)
> >  create mode 100644 drivers/misc/sram-dma-heap.c
> >
> > diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
> > index 9e4ad4d61f06..e6674e913168 100644
> > --- a/drivers/misc/Kconfig
> > +++ b/drivers/misc/Kconfig
> > @@ -448,6 +448,13 @@ config SRAM
> >  config SRAM_EXEC
> >       bool
> >
> > +config SRAM_DMA_HEAP
> > +     bool "Export on-chip SRAM pools using DMA-Heaps"
> > +     depends on DMABUF_HEAPS && SRAM
> > +     help
> > +       This driver allows the export of on-chip SRAM marked as both pool
> > +       and exportable to userspace using the DMA-Heaps interface.
>
> What will use this in userspace?
>

I could imagine a way it might be used.

Imagine a SoC like TI's AM64x series, where some cores (A53) run Linux
and others (R5F) are managed by remoteproc to
execute a RTOS. When it comes to efficiently exchanging large data
sets, the conventional method involves using rpmsg,
which has limitations due to message size and could potentially slow
down data transfer. However, an alternative
approach could be to allocate a sizable chunk of SRAM memory in
userspace. By utilizing memcpy() to copy data into
this memory, followed by a single rpmsg signal to notify the RTOS that
the data is ready, we can leverage the faster access
speed of SRAM compared to DDR from the remoteproc.

-- 
greets
--
Christian Gmeiner, MSc

https://christian-gmeiner.info/privacypolicy