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

[Adrian Hunter]

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.

> 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.