linux-kernel - Re: [PATCH v2 05/13] usb: musb: create debugfs directory under usb root

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Date:   Thu, 14 Nov 2019 08:02:34 -0600
From:   Bin Liu <b-liu@...com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:     Chunfeng Yun <chunfeng.yun@...iatek.com>,
        Felipe Balbi <balbi@...nel.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Peter Chen <Peter.Chen@....com>,
        Minas Harutyunyan <hminas@...opsys.com>,
        Cristian Birsan <cristian.birsan@...rochip.com>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Ludovic Desroches <ludovic.desroches@...rochip.com>,
        Kevin Cernekee <cernekee@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        <bcm-kernel-feedback-list@...adcom.com>,
        Daniel Mack <daniel@...que.org>,
        Haojian Zhuang <haojian.zhuang@...il.com>,
        Robert Jarzmik <robert.jarzmik@...e.fr>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Stephen Boyd <swboyd@...omium.org>,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        Colin Ian King <colin.king@...onical.com>,
        Biju Das <biju.das@...renesas.com>,
        Fabrizio Castro <fabrizio.castro@...renesas.com>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Yangtao Li <tiny.windzz@...il.com>,
        <linux-media@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-usb@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-mediatek@...ts.infradead.org>
Subject: Re: [PATCH v2 05/13] usb: musb: create debugfs directory under usb
 root

On Thu, Nov 14, 2019 at 11:20:18AM +0800, Greg Kroah-Hartman wrote:
> On Tue, Nov 12, 2019 at 09:28:57AM -0600, Bin Liu wrote:
> > Hi,
> > 
> > On Tue, Nov 12, 2019 at 02:51:51PM +0800, Chunfeng Yun wrote:
> > > Now the USB gadget subsystem can use the USB debugfs root directory,
> > > so move musb's directory from the root of the debugfs filesystem into
> > > the root of usb
> > 
> > My opinion is this move is unnecessary. I breaks existing debug tools or
> > documentation which is already published on Internet. 
> 
> Having a "root" directory for a single random driver seems like you are
> making your driver a "very important" thing in the overall scheme of the
> kernel, right?  What's wrong with using the usb subdirectory like all

Agree, it wasn't the right thing to do at the first place. But now
changing it adds support burden, because people very often refer to the
old information on the internet which no longer matches to the new
location. Basically, it is a cost of ABI change.

> other USB drivers use (after this patch series is merged)?  That feels
> like a much more "sane" way to handle the wide-open debugfs namespace.

Though I commented on this musb patch, my opinion is for this whole
series, either drop the whole series or apply the whole series.

> Yes, there are no rules when it comes to debugfs file names and
> locations, but let's try to be sane please.

Fine with me. I can still support questions such as "can't open
/sys/kernel/debug/musb-hdrc.0/testmode: No such file or directory".

-Bin.