Re: [PATCH] cxl: check decoder count for end device

[Dave Jiang <dave.jiang@intel.com>]

On 10/21/2022 2:17 PM, Dan Williams wrote:
> Dave Jiang wrote:
>> CXL spec rev3.0 8.2.4.19.1 added definition for up to 32 decoders. It also
>> indicates that for devices, only 10 decoders should be advertised. Add
>> check on number of decoders greater than 10 for devices and reset to 10 to
>> force spec compliance.
>>
>> Signed-off-by: Dave Jiang <dave.jiang@intel.com>
>> ---
>>   drivers/cxl/core/hdm.c |   16 +++++++++++++++-
>>   1 file changed, 15 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c
>> index d1d2caea5c62..1919d99d157e 100644
>> --- a/drivers/cxl/core/hdm.c
>> +++ b/drivers/cxl/core/hdm.c
>> @@ -71,9 +71,23 @@ EXPORT_SYMBOL_NS_GPL(devm_cxl_add_passthrough_decoder, CXL);
>>   static void parse_hdm_decoder_caps(struct cxl_hdm *cxlhdm)
>>   {
>>   	u32 hdm_cap;
>> +	int decoder_count;
>> +	struct device *dev = &cxlhdm->port->dev;
>>   
>>   	hdm_cap = readl(cxlhdm->regs.hdm_decoder + CXL_HDM_DECODER_CAP_OFFSET);
>> -	cxlhdm->decoder_count = cxl_hdm_decoder_count(hdm_cap);
>> +	decoder_count = cxl_hdm_decoder_count(hdm_cap);
>> +	/*
>> +	 * CXL spec rev3.0 8.2.4.19.1 indicates CXL devices shall not advertise
>> +	 * more than 10 decoders. Switches and Host Bridges may advertise up to
>> +	 * 32 decoders. Set the decoders to 10 for devices if more than 10 are
>> +	 * found.
>> +	 */
>> +	if (is_cxl_endpoint(cxlhdm->port) && decoder_count > 10) {
>> +		dev_warn(dev, "Reset decoders count (%d) to 10, spec violation!\n",
>> +			 decoder_count);
>> +		decoder_count = 10;
> I agree with the reporting, but not the limitation. The Robustness
> Principle says if allowing it does no harm, then let it through.
Ok I'll remove the reassigment.