linux-kernel - Re: [PATCH v1 0/4] Add tracing for SDHCI register access

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Message-ID: <20190419184013.GA145226@google.com>
Date:   Fri, 19 Apr 2019 12:40:13 -0600
From:   Raul Rangel <rrangel@...omium.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-trace-devel@...r.kernel.org, linux-mmc@...r.kernel.org,
        djkurtz@...omium.org, zwisler@...omium.org,
        Ludovic Barre <ludovic.barre@...com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Jisheng Zhang <Jisheng.Zhang@...aptics.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Faiz Abbas <faiz_abbas@...com>, linux-kernel@...r.kernel.org,
        Oleksij Rempel <linux@...pel-privat.de>,
        Liming Sun <lsun@...lanox.com>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        Ingo Molnar <mingo@...hat.com>,
        Prabu Thangamuthu <Prabu.T@...opsys.com>,
        Chunyan Zhang <chunyan.zhang@...soc.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Adrian Hunter <adrian.hunter@...el.com>
Subject: Re: [PATCH v1 0/4] Add tracing for SDHCI register access

On Thu, Apr 18, 2019 at 09:24:16AM +0300, Adrian Hunter wrote:
> On 12/04/19 5:50 PM, Raul Rangel wrote:
> > On Fri, Apr 12, 2019 at 09:26:44AM +0300, Adrian Hunter wrote:
> >> On 12/04/19 1:08 AM, Raul E Rangel wrote:
> >>> I was debugging a SDHC hardware bug and got tired of having to
> >>> translate the register values by hand. This patch set makes it so all
> >>> SDHC register read and write operations can be traced and easily read by
> >>> a human.
> >>
> >> While this might be useful for people unfamiliar with SDHCI, I am not sure
> >> it should be in the upstream kernel.
> > Can you help me understand your hesitation? Would you prefer removing the
> > pretty printing? Or would you prefer not having any trace events at all?
> 
> It is just cost/benefit.  I am not sure the cost of maintaining it is worth
> the benefit of having it upstream.
> 
Steven,
Since it seems this series won't be accepted upstream, would you still be
open to accepting patches for trace_print_register? I can work on adding
support to lib traceevent.

Thanks,
Raul
> > The xhci driver has a bunch of pretty print trace events that make it
> > invaluable when debugging.
> > https://github.com/torvalds/linux/blob/d7563ca5bfca53398e100eb74345c5d3ef06bf9d/drivers/usb/host/xhci.h#L2160
> > 
> >> Also, it doesn't seem ideal for every
> >> driver to add its own plumbing for such a feature.
> > What do you mean by every driver having to add it's own plumbing? Any
> > driver that uses sdhci_readX or sdhci_writeX get the functionality for
> > free.
> 
> I/O memory mappings are recorded for devices. e.g. /proc/iomem so it could
> be possible to add tracing for all I/O memory accesses via readx/writex etc,
> configurable / filterable by device id.