linux-kernel - RE: [PATCH 4/7] EDAC/mce_amd: extract node id from InstanceHi in IPID

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Date:   Tue, 10 Aug 2021 12:45:22 +0000
From:   "Chatradhi, Naveen Krishna" <NaveenKrishna.Chatradhi@....com>
To:     "Ghannam, Yazen" <Yazen.Ghannam@....com>
CC:     "linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "bp@...en8.de" <bp@...en8.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "mchehab@...nel.org" <mchehab@...nel.org>
Subject: RE: [PATCH 4/7] EDAC/mce_amd: extract node id from InstanceHi in IPID

[Public]

Hi Yazen

-----Original Message-----
From: Ghannam, Yazen <Yazen.Ghannam@....com> 
Sent: Thursday, July 29, 2021 10:03 PM
To: Chatradhi, Naveen Krishna <NaveenKrishna.Chatradhi@....com>
Cc: linux-edac@...r.kernel.org; x86@...nel.org; linux-kernel@...r.kernel.org; bp@...en8.de; mingo@...hat.com; mchehab@...nel.org
Subject: Re: [PATCH 4/7] EDAC/mce_amd: extract node id from InstanceHi in IPID

On Wed, Jun 30, 2021 at 08:58:25PM +0530, Naveen Krishna Chatradhi wrote:
> On AMD systems with SMCA banks on NONCPU nodes, the node id 
> information is available in the InstanceHI[47:44] of the IPID register.

The doesn't read well to me. I saw this as saying "bits 47:44 of the InstanceHi register". Also, the name of the field is "InstanceIdHi" in the documentation.

I think it'd be more clear to say "available in MCA_IPID[47:44] (InstanceIdHi)" or something similar. 
[naveenk:] Modified the commit message

> 
> Signed-off-by: Muralidhara M K <muralimk@....com>
> Signed-off-by: Naveen Krishna Chatradhi <nchatrad@....com>
> ---
>  drivers/edac/mce_amd.c | 15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/edac/mce_amd.c b/drivers/edac/mce_amd.c index 
> 27d56920b469..364dfb6e359d 100644
> --- a/drivers/edac/mce_amd.c
> +++ b/drivers/edac/mce_amd.c
> @@ -1049,6 +1049,7 @@ static void decode_smca_error(struct mce *m)
>  	enum smca_bank_types bank_type;
>  	const char *ip_name;
>  	u8 xec = XEC(m->status, xec_mask);
> +	u32 node_id = 0;

Why u32? Why not u16 to match topology_die_id() or int to match decode_dram_ecc()?
[naveenk:] Done, used int.

>  
>  	if (m->bank >= ARRAY_SIZE(smca_banks))
>  		return;
> @@ -1072,8 +1073,18 @@ static void decode_smca_error(struct mce *m)
>  	if (xec < smca_mce_descs[bank_type].num_descs)
>  		pr_cont(", %s.\n", smca_mce_descs[bank_type].descs[xec]);
>  
> -	if (bank_type == SMCA_UMC && xec == 0 && decode_dram_ecc)
> -		decode_dram_ecc(topology_die_id(m->extcpu), m);
> +	/*
> +	 * SMCA_UMC_V2 is used on the noncpu nodes, extract the node id
> +	 * from the InstanceHI[47:44] of the IPID register.
> +	 */
> +	if (bank_type == SMCA_UMC_V2 && xec == 0)
> +		node_id = ((m->ipid >> 44) & 0xF);
> +
> +	if (bank_type == SMCA_UMC && xec == 0)
> +		node_id = topology_die_id(m->extcpu);
> +
> +	if (decode_dram_ecc)
> +		decode_dram_ecc(node_id, m);

If decode_dram_ecc() is set, then this will call it on every MCA error that comes in. Rather we only want to call it on DRAM ECC errors.

You could do something like this:

	if (decode_dram_ecc && xec == 0) {
		u32 node_id = 0;

		if (bank_type == SMCA_UMC)
			node_id = XXX;
		else if (bank_type == SMCA_UMC_V2)
			node_id = YYY;
		else
			return;

		decode_dram_ecc(node_id, m);
	}

This is just an example. Maybe you can save an indentation level by negating those conditions and returning early, etc.
[naveenk:] modified the ladder.

Thanks,
Yazen
[naveenk:] Thank you.