Messages in this thread | | | Date | Wed, 3 Jan 2018 11:51:16 +0000 | From | Mark Brown <> | Subject | Re: [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] | |