Re: [PATCH - Omapzoom] [NAND] Add prefetch and DMA support

[David Brownell <david-b@pacbell.net>]

On Monday 08 September 2008, Kamat, Nishant wrote:
> +config MTD_NAND_OMAP_PREFETCH
> +       bool "GPMC prefetch support for NAND Flash device"
> +       depends on MTD_NAND && MTD_NAND_OMAP2
> +       default n
> +       help
> +        The NAND device can be accessed for Read/Write using GPMC PREFETCH engine
> +        to improve the performance.

Is there a reason this isn't always enabled, and the choice is just
whether to use DMA or not?


I'd be interested to see performance measurements for the three cases.

	- current/slow code
	- the readsw() update I sent previously
	- this "prefetch engine"

And I'd expect this "prefetch engine" code would also be improved by
using readsw() and writesw() when DMA isn't in use.

On one ARM926 I observed a 16% speedup *just* from switching from
slow byte-at-a-time PIO to using readsb ... this current code has
that same pessimization.

- Dave


> +
> +choice
> +       prompt "Prefetch engine support for GPMC"
> +       depends on MTD_NAND_OMAP_PREFETCH
> +       help
> +        The GPMC PREFETCH engine can be configured eigther in MPU interrupt mode
> +        or in DMA interrupt mode.
> +
> +config MTD_NAND_OMAP_PREFETCH_MPU
> +       depends on MTD_NAND_OMAP_PREFETCH
> +       bool "MPU mode always for spare area + MPU mode for main area"
> +       help
> +        Say y if... you want MPU interrupt mode for both spare area and main area accesses.
> +
> +config MTD_NAND_OMAP_PREFETCH_DMA
> +       depends on MTD_NAND_OMAP_PREFETCH
> +       bool "MPU mode always for spare area + DMA mode for main area"
> +       help
> +        Say y if... you want MPU interrupt mode for spare area and DMA mode for main
> +        area access.
> +
> +endchoice
> +


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