linux-kernel - Re: [PATCH 1/1] spi: atmel: fix corrupted data issue on SAM9 family SoCs

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Message-ID: <7c2de4d4-b5ec-ac12-77a2-8a9f1c47f023@microchip.com>
Date:   Fri, 23 Jun 2017 17:41:51 +0200
From:   Nicolas Ferre <nicolas.ferre@...rochip.com>
To:     Cyrille Pitchen <cyrille.pitchen@...rochip.com>,
        <broonie@...nel.org>, <linux-spi@...r.kernel.org>
CC:     <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/1] spi: atmel: fix corrupted data issue on SAM9 family
 SoCs

On 23/06/2017 at 17:39, Cyrille Pitchen wrote:
> This patch disables the use of the DMA for data transfer and forces the
> use of PIO transfers instead as a quick fixup to solve the cache aliasing
> issue on ARM9 based cores, which embeds a VIVT data cache.
> 
> Indeed in the case of VIVT data caches, it is not safe to call dma_map_*()
> functions to map buffers for DMA transfers when those buffers have been
> allocated by vmalloc() or from any DMA-unsafe area.
> 
> Further patches may propose a better solution based on the use of a bounce
> buffer at the SPI sub-system level but such solution needs more time to be
> discussed. Then the use of DMA transfers could be enabled again to improve
> the performances but before that, this patch already solves the issue.
> 
> Signed-off-by: Cyrille Pitchen <cyrille.pitchen@...rochip.com>

Yes:
Acked-by: Nicolas Ferre <nicolas.ferre@...rochip.com>

Thanks Cyrille.

Regards,

> ---
>  drivers/spi/spi-atmel.c | 24 +++++++++++++++++++++++-
>  1 file changed, 23 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/spi/spi-atmel.c b/drivers/spi/spi-atmel.c
> index 4e5e51fe6f73..f95da364c283 100644
> --- a/drivers/spi/spi-atmel.c
> +++ b/drivers/spi/spi-atmel.c
> @@ -269,6 +269,7 @@ struct atmel_spi_caps {
>  	bool	is_spi2;
>  	bool	has_wdrbt;
>  	bool	has_dma_support;
> +	bool	has_pdc_support;
>  };
>  
>  /*
> @@ -1425,7 +1426,28 @@ static void atmel_get_caps(struct atmel_spi *as)
>  
>  	as->caps.is_spi2 = version > 0x121;
>  	as->caps.has_wdrbt = version >= 0x210;
> +#ifdef CONFIG_SOC_SAM_V4_V5
> +	/*
> +	 * Atmel SoCs based on ARM9 (SAM9x) cores should not use spi_map_buf()
> +	 * since this later function tries to map buffers with dma_map_sg()
> +	 * even if they have not been allocated inside DMA-safe areas.
> +	 * On SoCs based on Cortex A5 (SAMA5Dx), it works anyway because for
> +	 * those ARM cores, the data cache follows the PIPT model.
> +	 * Also the L2 cache controller of SAMA5D2 uses the PIPT model too.
> +	 * In case of PIPT caches, there cannot be cache aliases.
> +	 * However on ARM9 cores, the data cache follows the VIVT model, hence
> +	 * the cache aliases issue can occur when buffers are allocated from
> +	 * DMA-unsafe areas, by vmalloc() for instance, where cache coherency is
> +	 * not taken into account or at least not handled completely (cache
> +	 * lines of aliases are not invalidated).
> +	 * This is not a theorical issue: it was reproduced when trying to mount
> +	 * a UBI file-system on a at91sam9g35ek board.
> +	 */
> +	as->caps.has_dma_support = false;
> +#else
>  	as->caps.has_dma_support = version >= 0x212;
> +#endif
> +	as->caps.has_pdc_support = version < 0x212;
>  }
>  
>  /*-------------------------------------------------------------------------*/
> @@ -1566,7 +1588,7 @@ static int atmel_spi_probe(struct platform_device *pdev)
>  		} else if (ret == -EPROBE_DEFER) {
>  			return ret;
>  		}
> -	} else {
> +	} else if (as->caps.has_pdc_support) {
>  		as->use_pdc = true;
>  	}
>  
> 


-- 
Nicolas Ferre