Re: [Qemu-devel] [PATCH V5 5/7] Add max device width parameter for NOR devices

[Peter Maydell <peter.maydell@linaro.org>]

On 5 December 2013 21:35, Roy Franz <roy.franz@linaro.org> wrote:
> For handling CFI and device ID reads, we need to not only know the
> width that a NOR flash device is configured for, but also its maximum
> width.  The maximum width addressing mode is used for multi-width
> parts no matter which width they are configured for.  The most common
> case is x16 parts that also support x8 mode.  When configured for x8
> operation these devices respond to CFI and device ID requests differently
> than native x8 NOR parts.

>      DEFINE_PROP_UINT64("sector-length", struct pflash_t, sector_len, 0),
>      DEFINE_PROP_UINT8("width", struct pflash_t, bank_width, 0),
>      DEFINE_PROP_UINT8("device-width", struct pflash_t, device_width, 0),
> +    DEFINE_PROP_UINT8("max-device-width", struct pflash_t, max_device_width, 0),

So I think that given we now have three width related properties
we could use a comment here about what they mean. Do I have
this right?

/* width here is the overall width of this QEMU device in bytes.
 * The QEMU device may be emulating a number of flash devices
 * wired up in parallel; the width of each individual flash
 * device should be specified via device-width. If the individual
 * devices have a maximum width which is greater than the width
 * they are being used for, this maximum width should be set via
 * max-device-width (which otherwise defaults to device-width).
 * So for instance a 32-bit wide QEMU flash device made from four
 * 16-bit flash devices used in 8-bit wide mode would be configured
 * with width = 4, device-width = 1, max-device-width = 2.
 *
 * If device-width is not specified we default to backwards
 * compatible behaviour which is a bad emulation of two
 * 16 bit devices making up a 32 bit wide QEMU device. This
 * is deprecated for new uses of this device.
 */

thanks
-- PMM