linux-kernel - Re: [PATCH 5/6] remoteproc: mtk_apu: Don't try to use the APU local RAM

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Date:   Tue, 21 Jul 2020 14:43:32 -0600
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Alexandre Bailon <abailon@...libre.com>
Cc:     ohad@...ery.com, bjorn.andersson@...aro.org, robh+dt@...nel.org,
        matthias.bgg@...il.com, linux-remoteproc@...r.kernel.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/6] remoteproc: mtk_apu: Don't try to use the APU local
 RAM

On Mon, Jul 13, 2020 at 03:29:26PM +0200, Alexandre Bailon wrote:
> Currently, this local RAM is not accessible from the CPU.
> If the CPU tries to access it, then the CPU will hang.
> 
> Remoteproc may try to use it when it load a firmware
> that has some sections in the local RAM.
> This workarounds the issue by skiping this section.
> 
> Signed-off-by: Alexandre Bailon <abailon@...libre.com>
> ---
>  drivers/remoteproc/mtk_apu_rproc.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/drivers/remoteproc/mtk_apu_rproc.c b/drivers/remoteproc/mtk_apu_rproc.c
> index 565b3adca5de..e16d3258a785 100644
> --- a/drivers/remoteproc/mtk_apu_rproc.c
> +++ b/drivers/remoteproc/mtk_apu_rproc.c
> @@ -57,6 +57,9 @@
>  #define CORE_DEFAULT2_SPIDEN			BIT(0)
>  #define CORE_XTENSA_ALTRESETVEC			(0x000001F8)
>  
> +#define DRAM0_START				(0x7ff00000)
> +#define IRAM0_END				(0x7ff80000)
> +
>  struct mtk_vpu_rproc {
>  	struct device *dev;
>  	struct rproc *rproc;
> @@ -139,6 +142,7 @@ static void mtk_vpu_rproc_kick(struct rproc *rproc, int vqid)
>  
>  int mtk_vpu_elf_sanity_check(struct rproc *rproc, const struct firmware *fw)
>  {
> +	struct mtk_vpu_rproc *vpu_rproc = rproc->priv;
>  	const u8 *elf_data = fw->data;
>  	struct elf32_hdr *ehdr;
>  	struct elf32_phdr *phdr;
> @@ -156,6 +160,16 @@ int mtk_vpu_elf_sanity_check(struct rproc *rproc, const struct firmware *fw)
>  		/* Remove empty PT_LOAD section */
>  		if (phdr->p_type == PT_LOAD && !phdr->p_paddr)
>  			phdr->p_type = PT_NULL;
> +		/*
> +		 * Workaround: Currently, the CPU can't access to the APU
> +		 * local RAM. This removes the local RAM section from the
> +		 * firmware. Please note that may cause some issues.
> +		 */
> +		if (phdr->p_paddr >= DRAM0_START && phdr->p_paddr < IRAM0_END) {
> +			dev_warn_once(vpu_rproc->dev,
> +				      "Skipping the APU local RAM section\n");
> +			phdr->p_type = PT_NULL;

We can't selectively decide to not load sections of a program due to a platform
driver shortcoming.  Either a real solution is found or booting the remote
processor is interrupted, with a strong incline toward the former.

I guess you're dealing with tightly coupled memory or on-chip RAM areas -
both are accessed on other platform using ioremap_wc() or devm_ioremap_wc().
You might want to try doing what Suman has done in this patchset [1], with
specific attention to TCMs and SRAM.

Thanks,
Mathieu

[1]. https://patchwork.kernel.org/project/linux-remoteproc/list/?series=310325

> +		}
>  	}
>  
>  	return 0;
> -- 
> 2.26.2
>