lkml.org 
[lkml]   [2018]   [Jan]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 2/3] dt-bindings: mtd: atmel-quadspi: add an optional property 'dmacap,memcpy'
On Wed, Dec 27, 2017 at 10:40:00PM +0100, Cyrille Pitchen wrote:
> Le 27/12/2017 à 00:23, Rob Herring a écrit :
> > On Sun, Dec 24, 2017 at 05:36:05AM +0100, Cyrille Pitchen wrote:

> >> +Optional properties:
> >> +- dmacap,memcpy: Reserve a DMA channel to perform DMA memcpy() between the
> >> + system memory and the QSPI mapped memory.

> > How is this a h/w property? Why would I not want to always enable DMA if
> > possible?

> The number of DMA channels is limited for a given SoC. This number may be
> lower than the number of enabled controllers (spi, i2c, qspi, aes, sha,
> des, sdmmc, usart, ...).

> So we use a DT property to explicitly tell the matching drivers to request
> and reserved the DMA channels they need. This policy is not driver or even
> SoC specific but board specific. It's very common to reserved DMA channels
> for the most used or most performance dependent controllers, setting the
> relevant properties in the device-tree then restricting remaining
> controllers to their PIO mode.

Why can't we just time share the DMA channels at runtime, why do we need
this static allocation?
[unhandled content-type:application/pgp-signature]
\
 
 \ /
  Last update: 2018-01-03 12:51    [W:0.037 / U:5.848 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site