netdev - Re: [PATCH v9 03/27] cxl: add capabilities field to cxl_dev_state and cxl

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Message-ID: <ffbca9f2-80fa-530a-9ec1-9f811ee61e38@amd.com>
Date: Fri, 3 Jan 2025 07:20:48 +0000
From: Alejandro Lucero Palau <alucerop@....com>
To: Jonathan Cameron <Jonathan.Cameron@...wei.com>,
 alejandro.lucero-palau@....com
Cc: linux-cxl@...r.kernel.org, netdev@...r.kernel.org,
 dan.j.williams@...el.com, edward.cree@....com, davem@...emloft.net,
 kuba@...nel.org, pabeni@...hat.com, edumazet@...gle.com, dave.jiang@...el.com
Subject: Re: [PATCH v9 03/27] cxl: add capabilities field to cxl_dev_state and
 cxl_port


On 1/2/25 14:36, Jonathan Cameron wrote:
> On Mon, 30 Dec 2024 21:44:21 +0000
> <alejandro.lucero-palau@....com> wrote:
>
>> From: Alejandro Lucero <alucerop@....com>
>>
>> Type2 devices have some Type3 functionalities as optional like an mbox
>> or an hdm decoder, and CXL core needs a way to know what an CXL accelerator
>> implements.
>>
>> Add a new field to cxl_dev_state for keeping device capabilities as
>> discovered during initialization. Add same field to cxl_port as registers
>> discovery is also used during port initialization.
>>
>> Signed-off-by: Alejandro Lucero <alucerop@....com>
>> Reviewed-by: Ben Cheatham <benjamin.cheatham@....com>
>> Reviewed-by: Fan Ni <fan.ni@...sung.com>
> Comment in thread on v8.  I don't see a reason to have any specific
> bitmap length - just use a final entry in the enum without a value set
> to let us know how long it actually is.


I could do this but it implies to clear/zeroing the bitmaps with the 
final entry value and to mask bitmaps with that when comparing them.

I tried to avoid the masking, and it led to that use of sizeof and then 
CXL_MAX_CAPS=64.


> Using the bit / bitmap functions should work fine without constraining
> that to any particular value - also allowing for greater than 64 entries
> with no need to fix up call sites etc.
>
>
>> diff --git a/drivers/cxl/core/regs.c b/drivers/cxl/core/regs.c
>> index 59cb35b40c7e..144ae9eb6253 100644
>> --- a/drivers/cxl/core/regs.c
>> +++ b/drivers/cxl/core/regs.c
>> @@ -4,6 +4,7 @@
>> +enum cxl_dev_cap {
>> +	/* capabilities from Component Registers */
>> +	CXL_DEV_CAP_RAS,
>> +	CXL_DEV_CAP_HDM,
>> +	/* capabilities from Device Registers */
>> +	CXL_DEV_CAP_DEV_STATUS,
>> +	CXL_DEV_CAP_MAILBOX_PRIMARY,
>> +	CXL_DEV_CAP_MEMDEV,
>> +	CXL_MAX_CAPS = 64
> As in v8. I'm not seeing any reason for this.  If you need
> a bitmap to be a particular number of unsigned longs, then that
> code should be fixed. (only exception being compile time constant
> bitmaps where this is tricky to do!)
>
> Obviously I replied with that to v8 after you posted this
> so time machines aside no way you could have acted on it yet.
>
>
> Jonathan
>
>> +};
>> +
>>   struct cxl_dev_state;
>>   struct device;
>>