Subject: Re: [PATCH v4 07/26] sfc: use cxl api for regs setup and checking

From: Alejandro Lucero Palau <[email-masked]>
Date: Fri, 18 Oct 2024 16:07:22 +0100

On 10/17/24 22:49, Ben Cheatham wrote:
> On 10/17/24 11:52 AM, [email-masked] wrote:
>> From: Alejandro Lucero <[email-masked]>
>>
>> Use cxl code for registers discovery and mapping.
>>
>> Validate capabilities found based on those registers against expected
>> capabilities.
>>
>> Signed-off-by: Alejandro Lucero <[email-masked]>
>> ---
>>   drivers/net/ethernet/sfc/efx_cxl.c | 19 +++++++++++++++++++
>>   1 file changed, 19 insertions(+)
>>
>> diff --git a/drivers/net/ethernet/sfc/efx_cxl.c b/drivers/net/ethernet/sfc/efx_cxl.c
>> index fb3eef339b34..749aa97683fd 100644
>> --- a/drivers/net/ethernet/sfc/efx_cxl.c
>> +++ b/drivers/net/ethernet/sfc/efx_cxl.c
>> @@ -22,6 +22,8 @@ int efx_cxl_init(struct efx_nic *efx)
>>   {
>>   #if IS_ENABLED(CONFIG_CXL_BUS)
>>   	struct pci_dev *pci_dev = efx->pci_dev;
>> +	DECLARE_BITMAP(expected, CXL_MAX_CAPS);
>> +	DECLARE_BITMAP(found, CXL_MAX_CAPS);
>>   	struct efx_cxl *cxl;
>>   	struct resource res;
>>   	u16 dvsec;
>> @@ -64,6 +66,23 @@ int efx_cxl_init(struct efx_nic *efx)
>>   		goto err2;
>>   	}
>>   
>> +	rc = cxl_pci_accel_setup_regs(pci_dev, cxl->cxlds);
>> +	if (rc) {
>> +		pci_err(pci_dev, "CXL accel setup regs failed");
>> +		goto err2;
>> +	}
>> +
>> +	bitmap_clear(expected, 0, BITS_PER_TYPE(unsigned long));
> In some places you use BITS_PER_TYPE(unsigned long) for the size of the capabilities bitmap,
> while in others you use CXL_MAX_CAPS. Right now it isn't an issue since CXL_MAX_CAPS is way
> smaller than the size of an unsigned long, but I seem to remember Jonathan suggesting this
> for future proofing. So, I would suggest setting CXL_MAX_CAPS = BITS_PER_TYPE(unsigned long)
> and using CXL_MAX_CAPS everywhere (or just using CXL_MAX_CAPS as-is). Then, when/if there
> are more capabilities we can just increase what CXL_MAX_CAPS is set to.

The reason for using this BITS_PER_TYPE here is because with 
CXL_MAX_CAPS, as it is defined now, it would not clear those bits not 
covered by the current value. Defining CXL_MAX_CAPS as 32 in the enum 
would solce thais problem. I think that is cleaner than doing any 
masking depending on CXL_MAX_CAPS so I will do so in v5.

Thanks

>> +	bitmap_set(expected, CXL_DEV_CAP_HDM, 1);
>> +	bitmap_set(expected, CXL_DEV_CAP_RAS, 1);
>> +
>> +	if (!cxl_pci_check_caps(cxl->cxlds, expected, found)) {
>> +		pci_err(pci_dev,
>> +			"CXL device capabilities found(%08lx) not as expected(%08lx)",
>> +			*found, *expected);
>> +		goto err2;
>> +	}
>> +
>>   	efx->cxl = cxl;
>>   #endif
>>