linux-kernel - Re: [PATCH] EDAC: altera: Add SDRAM ECC check for U-Boot

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Date:   Thu, 10 Mar 2022 08:19:24 -0600
From:   Dinh Nguyen <dinguyen@...nel.org>
To:     niravkumar.l.rabara@...el.com, bp@...en8.de, mchehab@...nel.org,
        tony.luck@...el.com, james.morse@....com, rric@...nel.org,
        linux-edac@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH] EDAC: altera: Add SDRAM ECC check for U-Boot



On 3/4/22 19:41, niravkumar.l.rabara@...el.com wrote:
> From: Rabara Niravkumar L <niravkumar.l.rabara@...el.com>
> 
> A bug in legacy U-Boot causes a crash during SDRAM boot if ECC
> is not enabled in the bitstream but enabled in the Linux config.
> 
> Memory mapped read of the ECC Enabled bit was only enabled
> if U-Boot determined ECC was enabled in the bitstream.
> 
> The Linux driver checks the ECC enable bit using a memory map
> read. In the ECC disabled bitstream case, U-Boot didn't
> enable ECC register memory map reads and since they are not
> allowed this results in a crash.
> 
> This patch always reads the ECC Enable register through a
> SMC call which is always allowed and it works with legacy
> and current U-Boot.
> 
> Signed-off-by: Rabara Niravkumar L <niravkumar.l.rabara@...el.com>
> ---
>   drivers/edac/altera_edac.c | 40 +++++++++++++++++++++++++++++++++++++-
>   1 file changed, 39 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/edac/altera_edac.c b/drivers/edac/altera_edac.c
> index 5dd29789f97d..e7e8e624a436 100644
> --- a/drivers/edac/altera_edac.c
> +++ b/drivers/edac/altera_edac.c
> @@ -1083,8 +1083,46 @@ static int __init __maybe_unused altr_init_a10_ecc_device_type(char *compat)
>   
>   #ifdef CONFIG_EDAC_ALTERA_SDRAM
>   
> +/*
> + * A legacy U-Boot bug only enabled memory mapped access to the ECC Enable
> + * register if ECC is enabled. Linux checks the ECC Enable register to
> + * determine ECC status.
> + * Use an SMC call (which always works) to determine ECC enablement.
> + */
> +static int altr_s10_sdram_check_ecc_deps(struct altr_edac_device_dev *device)
> +{
> +	const struct edac_device_prv_data *prv = device->data;
> +	unsigned long sdram_ecc_addr;
> +	struct arm_smccc_res result;
> +	struct device_node *np;
> +	phys_addr_t sdram_addr;
> +	u32 read_reg;
> +	int ret;
> +
> +	np = of_find_compatible_node(NULL, NULL, "altr,sdr-ctl");
> +	if (!np)
> +		goto sdram_err;
> +
> +	sdram_addr = of_translate_address(np, of_get_address(np, 0,
> +							     NULL, NULL));
> +	of_node_put(np);
> +	sdram_ecc_addr = (unsigned long)sdram_addr + prv->ecc_en_ofst;
> +	arm_smccc_smc(INTEL_SIP_SMC_REG_READ, sdram_ecc_addr,
> +		      0, 0, 0, 0, 0, 0, &result);
> +	read_reg = (unsigned int)result.a1;
> +	ret = (int)result.a0;
> +	if (!ret && (read_reg & prv->ecc_enable_mask))
> +		return 0;
> +
> +sdram_err:
> +	edac_printk(KERN_ERR, EDAC_DEVICE,
> +		    "%s: No ECC present or ECC disabled.\n",
> +		    device->edac_dev_name);
> +	return -ENODEV;
> +}
> +
>   static const struct edac_device_prv_data s10_sdramecc_data = {
> -	.setup = altr_check_ecc_deps,
> +	.setup = altr_s10_sdram_check_ecc_deps,
>   	.ce_clear_mask = ALTR_S10_ECC_SERRPENA,
>   	.ue_clear_mask = ALTR_S10_ECC_DERRPENA,
>   	.ecc_enable_mask = ALTR_S10_ECC_EN,

Acked-by: Dinh Nguyen <dinguyen@...nel.org>