linux-kernel - Re: [PATCH v4] ufs: core: print UFSHCD capabilities in controller's sysfs node

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Date:   Mon, 1 Aug 2022 14:42:57 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Daniil Lunev <dlunev@...omium.org>
Cc:     Adrian Hunter <adrian.hunter@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Avri Altman <avri.altman@....com>,
        Bean Huo <beanhuo@...ron.com>, Can Guo <cang@...eaurora.org>,
        Daejun Park <daejun7.park@...sung.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        Sohaib Mohamed <sohaib.amhmd@...il.com>,
        Stanley Chu <stanley.chu@...iatek.com>,
        linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org
Subject: Re: [PATCH v4] ufs: core: print UFSHCD capabilities in controller's
 sysfs node

On 8/1/22 14:29, Daniil Lunev wrote:
>> Please change "can not / can be enabled" into "is not supported by the
>> host controller / is supported by the host controller".
>
> That would be incorrect. The "caps" variable semantics is a bit weird
> in the sense that it is used at times to convey "active" 
> capabilities, not just supported one. For example, for the 
> writebooster capability to be present in caps, first controller 
> driver should indicate it is ready to support it, then the part that 
> is attached to the host controller has to indicate support in the 
> device descriptor, then WB has to be configured and its lifetime
> should not be exhausted. If any of those parameters are not
> satisfied, the capability will be removed from the set despite 
> generally being supported. I am not sure how to properly word it, but
> just saying "controller supports it" would be counter-factual
> (especially since the controller doesn't really knows anything about
> writebooster per-se, it is part's functionality). What would be
> suggested wording in that case?
Given the above I think we can keep the current wording. This also makes 
me wonder why the UFSHCD_CAP_WB_EN flag occurs in the hba->caps member 
variable. That member variable is used to track controller capabilities. 
My understanding is that the WriteBooster functionality is a UFS device 
feature and also that no host controller support is required to control 
the WriteBooster feature.

Thanks,

Bart.