Re: [PATCH 3/3] ARM: OMAP: AM35xx: fix UART4 softreset

Mark A. Greer
2012-05-10T19:37:30Z

On Thu, May 10, 2012 at 11:29:19AM -0600, Paul Walmsley wrote:
> During kernel init, the AM3505/AM3517 UART4 cannot complete its softreset:
>
> omap_hwmod: uart4: softreset failed (waited 10000 usec)
>
> This also results in another warning later in the boot process:
>
> omap_hwmod: uart4: enabled state can only be entered from initialized, idle, or disabled state
>
> >From empirical observation, the AM35xx UART4 IP block requires either
> uart1_fck or uart2_fck to be enabled while UART4 resets. Otherwise
> the reset will never complete. So this patch adds uart1_fck as an
> optional clock for UART4 and adds the appropriate hwmod flag to cause
> uart1_fck to be enabled during the reset process. (The choice of
> uart1_fck over uart2_fck was arbitrary.)
>
> Unfortunately this observation raises many questions. Is it necessary
> for uart1_fck or uart2_fck to be controlled with uart4_fck for the
> UART4 to work correctly? What exactly do the AM35xx UART4 clock
> tree and the related PRCM idle management FSMs look like? If anyone
> has the ability to answer these questions through empirical functional
> testing, or hardware information from the AM35xx designers, it would
> be greatly appreciated.
>
> Cc: Benoît Cousson <b-cousson@ti.com>
> Cc: Kyle Manna <kyle.manna@fuel7.com>
> Cc: Mark A. Greer <mgreer@animalcreek.com>
> Cc: Ranjith Lohithakshan <ranjithl@ti.com>
> Signed-off-by: Paul Walmsley <paul@pwsan.com>

Acked-by: Mark A. Greer <mgreer@animalcreek.com>
(on an am3517evm)

Mark
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