linux-kernel - Re: [PATCH V13 05/10] mmc: cqhci: support for command queue enabled host

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Date:   Thu, 9 Nov 2017 13:26:05 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Adrian Hunter <adrian.hunter@...el.com>
Cc:     Ulf Hansson <ulf.hansson@...aro.org>,
        linux-mmc <linux-mmc@...r.kernel.org>,
        linux-block <linux-block@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Bough Chen <haibo.chen@....com>,
        Alex Lemberg <alex.lemberg@...disk.com>,
        Mateusz Nowak <mateusz.nowak@...el.com>,
        Yuliy Izrailov <Yuliy.Izrailov@...disk.com>,
        Jaehoon Chung <jh80.chung@...sung.com>,
        Dong Aisheng <dongas86@...il.com>,
        Das Asutosh <asutoshd@...eaurora.org>,
        Zhangfei Gao <zhangfei.gao@...il.com>,
        Sahitya Tummala <stummala@...eaurora.org>,
        Harjani Ritesh <riteshh@...eaurora.org>,
        Venu Byravarasu <vbyravarasu@...dia.com>,
        Shawn Lin <shawn.lin@...k-chips.com>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH V13 05/10] mmc: cqhci: support for command queue enabled host

On Wed, Nov 8, 2017 at 3:14 PM, Adrian Hunter <adrian.hunter@...el.com> wrote:
> On 08/11/17 11:22, Linus Walleij wrote:
>> On Fri, Nov 3, 2017 at 2:20 PM, Adrian Hunter <adrian.hunter@...el.com> wrote:

>> (...)

>>> +EXPORT_SYMBOL(cqhci_resume);
>>
>> Why would the CQE case require special suspend/resume
>> functionality?
>
> Seems like a very strange question.

Please realize that patch review is partly about education.

Educating me or anyone about your patch set involves
being humbe and not seeing your peers as lesser.

Making your reviewer feel stupid by saying the ask
"strange" or outright stupid questions is not helping
your cause.

> Obviously CQHCI has to be configured
> after suspend.

Yeah. I think I misunderstood is such that:

> Also please don't confuse CQE and CQHCI.  CQHCI is an implementation of a
> CQE.  We currently do not expect to have another implementation, but it is
> not impossible.

OK now you educated me, see it's not that hard without
using belitteling language.

>> This seems two much like on the side CQE-silo engineering,
>> just use the device .[runtime]_suspend/resume callbacks like
>> everyone else, make it possible for the host to figure out
>> if it is in CQE mode or not (I guess it should know already
>> since cqhci .enable() has been called?) and handle it
>> from there.
>
> That is how it works!  The host controller has to decide how to handle
> suspend / resume.

OK.

> cqhci_suspend() / cqhci_resume() are helper functions that the host
> controller can use, but doesn't have to.

OK.

>> Why would CQE hosts need special accessors and the rest
>> of the host not need it?
>
> Special accessors can be used to fix up registers that don't work exactly
> the way the standard specified.

Yeah this is fine as it is for CQHCI, I didn't get that
part :)

>> ->enable and ->disable() for just CQE seem reasonable.
>> But that leaves just two new ops.
>>
>> So why not just put .cqe_enable() and .cqe_disable()
>> ops into mmc_host_ops as optional and be done with it?
>
> Ok so you are not understanding this at all.

No I did not get it. But I do now (I think).

> As a CQE implementation, CQHCI interfaces with the upper layers through the
> CQE ops etc.
>
> But CQHCI also has to work with any host controller driver, so it needs an
> interface for that, which is what cqhci_host_ops is for.  All the ops serve
> useful purposes.
(...)
> The whole point is to prove a library that can work with any host controller
> driver.  That means it must provide functions and callbacks.

OK

>> I think the above approach to put any CQE-specific callbacks
>> directly into the struct mmc_host_ops is way more viable.
>
> Nothing to do with CQE.  This is CQHCI.  Please try to get the difference.

I am trying, please try to think about your language.

>> If special CQE init is needed, why a special cqhci_init()
>> call? And cqhci_pltfm_init()? It's confusing. Can't
>> you just call this by default from the core if the host is
>> CQE capable? Ass a .cqhci_init() callback into mmc_host_ops
>> if need be.
>
> Yeah, so CQHCI is just one of theoretically any number of CQE
> implementations.  This has nothing to do with the core.  It is entirely up
> to the host driver.  cqhci_pltfm_init() allows the mmio space to be defined
> by platform resources, whereas cqhci_init() does all the rest of the
> initialization.

It's fair.

Yours,
Linus Walleij