Re: [PATCH v2 02/21] dma: add dma_sync nop stubs for PBL

[Sascha Hauer <sha@pengutronix.de>]

On Thu, Jun 09, 2022 at 07:59:03AM +0200, Ahmad Fatoum wrote:
> We can implement dma_sync functions as compiler barriers when we are
> certain that the buffers are in coherent/uncached memory, e.g. because
> MMU is only enabled in barebox_arm_entry which hasn't run yet.
> 
> This will come in handy when doing mailbox communication in PBL on the
> Raspberry Pi.
> 
> Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
> ---
>  include/dma.h | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/include/dma.h b/include/dma.h
> index 90f9254ea80f..aeaba7d9316d 100644
> --- a/include/dma.h
> +++ b/include/dma.h
> @@ -8,6 +8,7 @@
>  
>  #include <malloc.h>
>  #include <xfuncs.h>
> +#include <pbl.h>
>  #include <linux/kernel.h>
>  
>  #include <dma-dir.h>
> @@ -56,12 +57,30 @@ static inline int dma_mapping_error(struct device_d *dev, dma_addr_t dma_addr)
>  		(dev->dma_mask && dma_addr > dev->dma_mask);
>  }
>  
> +#ifndef __PBL__
>  /* streaming DMA - implement the below calls to support HAS_DMA */
>  void dma_sync_single_for_cpu(dma_addr_t address, size_t size,
>  			     enum dma_data_direction dir);
>  
>  void dma_sync_single_for_device(dma_addr_t address, size_t size,
>  				enum dma_data_direction dir);
> +#else
> +/*
> + * assumes buffers are in coherent/uncached memory, e.g. because
> + * MMU is only enabled in barebox_arm_entry which hasn't run yet.
> + */
> +static inline void dma_sync_single_for_cpu(dma_addr_t address, size_t size,
> +			     enum dma_data_direction dir)
> +{
> +	barrier_data((void *)address);
> +}
> +
> +static inline void dma_sync_single_for_device(dma_addr_t address, size_t size,
> +				enum dma_data_direction dir)
> +{
> +	barrier_data((void *)address);
> +}
> +#endif

This breaks compilation of socfpga-arria10_defconfig. We have these
stubs in arch/arm/include/asm/dma.h as well inside a #ifndef CONFIG_MMU.

Sascha

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