netdev - Re: [PATCH v2 04/15] cxl: add capabilities field to cxl_dev

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Message-ID: <7dbcdb5d-3734-8e32-afdc-72d898126a0c@amd.com>
Date: Tue, 23 Jul 2024 14:43:24 +0100
From: Alejandro Lucero Palau <alucerop@....com>
To: Dave Jiang <dave.jiang@...el.com>, alejandro.lucero-palau@....com,
 linux-cxl@...r.kernel.org, netdev@...r.kernel.org, dan.j.williams@...el.com,
 martin.habets@...inx.com, edward.cree@....com, davem@...emloft.net,
 kuba@...nel.org, pabeni@...hat.com, edumazet@...gle.com,
 richard.hughes@....com
Subject: Re: [PATCH v2 04/15] cxl: add capabilities field to cxl_dev_state


On 7/19/24 20:01, Dave Jiang wrote:
>
>>   
>> -static int cxl_probe_regs(struct cxl_register_map *map)
>> +static int cxl_probe_regs(struct cxl_register_map *map, uint8_t caps)
>>   {
>>   	struct cxl_component_reg_map *comp_map;
>>   	struct cxl_device_reg_map *dev_map;
>> @@ -437,11 +437,12 @@ static int cxl_probe_regs(struct cxl_register_map *map)
>>   	case CXL_REGLOC_RBI_MEMDEV:
>>   		dev_map = &map->device_map;
>>   		cxl_probe_device_regs(host, base, dev_map);
>> -		if (!dev_map->status.valid || !dev_map->mbox.valid ||
>> +		if (!dev_map->status.valid ||
>> +		    ((caps & CXL_DRIVER_CAP_MBOX) && !dev_map->mbox.valid) ||
>>   		    !dev_map->memdev.valid) {
>>   			dev_err(host, "registers not found: %s%s%s\n",
>>   				!dev_map->status.valid ? "status " : "",
>> -				!dev_map->mbox.valid ? "mbox " : "",
>> +				((caps & CXL_DRIVER_CAP_MBOX) && !dev_map->mbox.valid) ? "mbox " : "",
> According to the r3.1 8.2.8.2.1, the device status registers and the primary mailbox registers are both mandatory if regloc id=3 block is found. So if the type2 device does not implement a mailbox then it shouldn't be calling cxl_pci_setup_regs(pdev, CXL_REGLOC_RBI_MEMDEV, &map) to begin with from the driver init right? If the type2 device defines a regblock with id=3 but without a mailbox, then isn't that a spec violation?
>
> DJ


Right. The code needs to support the possibility of a Type2 having a 
mailbox, and if it is not supported, the rest of the dvsec regs 
initialization needs to be performed. This is not what the code does 
now, so I'll fix this.


A wider explanation is, for the RFC I used a test driver based on QEMU 
emulating a Type2 which had a CXL Device Register Interface defined 
(03h) but not a CXL Device Capability with id 2 for the primary mailbox 
register, breaking the spec as you spotted.


Thanks.