Re: [PATCHv2 12/12] ARM: OMAP4: hwmod data: do not enable or reset the McPDM during kernel init

["Péter Ujfalusi" <peter.ujfalusi@ti.com>]

Hi Paul,

On 10/30/2012 05:05 AM, Paul Walmsley wrote:
> omap_hwmod: mcpdm: cannot be enabled for reset (3)
> 
> The McPDM on OMAP4 can only receive its functional clock from an
> off-chip source.  This source is not guaranteed to be present on the
> board, and when present, it is controlled by I2C.  This would
> introduce a board dependency to the early hwmod code which it was not
> designed to handle.  Also, neither the driver for this off-chip clock
> provider nor the I2C code is available early in boot when the hwmod
> code is attempting to enable and reset IP blocks.  This effectively
> makes it impossible to enable and reset this device during hwmod init.
> 
> At its core, this patch is a workaround for an OMAP hardware problem.
> It should be possible to configure the OMAP to provide any IP block's
> functional clock from an on-chip source.  (This is true for almost
> every IP block on the chip.  As far as I know, McPDM is the only
> exception.)  If the kernel cannot reset and configure IP blocks, it
> cannot guarantee a sane SoC state.  Relying on an optional off-chip
> clock also creates a board dependency which is beyond the scope of the
> early hwmod code.
> 
> This patch works around the issue by marking the McPDM hwmod record
> with the HWMOD_EXT_OPT_MAIN_CLK flag.  This prevents the hwmod
> code from touching the device early during boot.
> 
> Signed-off-by: Paul Walmsley <paul@pwsan.com>
> Cc: Péter Ujfalusi <peter.ujfalusi@ti.com>
> Cc: Benoît Cousson <b-cousson@ti.com>

Acked-by: Peter Ujfalusi <peter.ujfalusi@ti.com>

> ---
>  arch/arm/mach-omap2/omap_hwmod_44xx_data.c |    8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/arch/arm/mach-omap2/omap_hwmod_44xx_data.c b/arch/arm/mach-omap2/omap_hwmod_44xx_data.c
> index 652d028..7bddfa5 100644
> --- a/arch/arm/mach-omap2/omap_hwmod_44xx_data.c
> +++ b/arch/arm/mach-omap2/omap_hwmod_44xx_data.c
> @@ -2125,6 +2125,14 @@ static struct omap_hwmod omap44xx_mcpdm_hwmod = {
>  	.name		= "mcpdm",
>  	.class		= &omap44xx_mcpdm_hwmod_class,
>  	.clkdm_name	= "abe_clkdm",
> +	/*
> +	 * It's suspected that the McPDM requires an off-chip main
> +	 * functional clock, controlled via I2C.  This IP block is
> +	 * currently reset very early during boot, before I2C is
> +	 * available, so it doesn't seem that we have any choice in
> +	 * the kernel other than to avoid resetting it.
> +	 */
> +	.flags		= HWMOD_EXT_OPT_MAIN_CLK,
>  	.mpu_irqs	= omap44xx_mcpdm_irqs,
>  	.sdma_reqs	= omap44xx_mcpdm_sdma_reqs,
>  	.main_clk	= "mcpdm_fck",
> 


-- 
Péter
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