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Date: Thu, 28 Mar 2024 16:40:58 -0700
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From: Daniel Ferguson <danielf@os.amperecomputing.com>
Subject: Re: [RFC PATCH v7 10/12] ACPI:RAS2: Add common library for RAS2 PCC
 interfaces
To: shiju.jose@huawei.com, linux-cxl@vger.kernel.org,
 linux-acpi@vger.kernel.org, linux-mm@kvack.org, dan.j.williams@intel.com,
 dave@stgolabs.net, jonathan.cameron@huawei.com, dave.jiang@intel.com,
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Cc: linux-edac@vger.kernel.org, linux-kernel@vger.kernel.org,
 david@redhat.com, Vilas.Sridharan@amd.com, leo.duran@amd.com,
 Yazen.Ghannam@amd.com, rientjes@google.com, jiaqiyan@google.com,
 tony.luck@intel.com, Jon.Grimm@amd.com, dave.hansen@linux.intel.com,
 rafael@kernel.org, lenb@kernel.org, naoya.horiguchi@nec.com,
 james.morse@arm.com, jthoughton@google.com, somasundaram.a@hpe.com,
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 mike.malvestuto@intel.com, gthelen@google.com,
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 kangkang.shen@futurewei.com, wanghuiqiang@huawei.com, linuxarm@huawei.com,
 wbs@os.amperecomputing.com
References: <20240223143723.1574-1-shiju.jose@huawei.com>
 <20240223143723.1574-11-shiju.jose@huawei.com>
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> +static int ras2_check_pcc_chan(struct ras2_context *ras2_ctx)
> +{
> +	struct acpi_ras2_shared_memory  __iomem *generic_comm_base = ras2_ctx->pcc_comm_addr;
> +	ktime_t next_deadline = ktime_add(ktime_get(), ras2_ctx->deadline);
> +
> +	while (!ktime_after(ktime_get(), next_deadline)) {
> +		/*
> +		 * As per ACPI spec, the PCC space wil be initialized by
> +		 * platform and should have set the command completion bit when
> +		 * PCC can be used by OSPM
> +		 */
> +		if (readw_relaxed(&generic_comm_base->status) & RAS2_PCC_CMD_COMPLETE)
> +			return 0;

We should consider adding error checking here. In a modification of this
driver in our enabling efforts, we are checking bit 2 in the status register
for errors. For example, in our FW, we will set bit 2 if you try to 
disable an
already disabled scrub.
> +		/*
> +		 * Reducing the bus traffic in case this loop takes longer than
> +		 * a few retries.
> +		 */
> +		udelay(10);
> +	}
> +
> +	return -EIO;
> +}