[PATCH 2/3] dt-bindings: mtd: atmel-quadspi: add an optional property 'dmacap,memcpy'

Mark Brown broonie at kernel.org
Wed Jan 3 03:51:16 PST 2018

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?  
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 488 bytes
Desc: not available
URL: <http://lists.infradead.org/pipermail/linux-mtd/attachments/20180103/5c64fe2b/attachment.sig>

More information about the linux-mtd mailing list