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Date:   Sat, 30 May 2020 23:17:05 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     sergei.shtylyov@...entembedded.com, bgolaszewski@...libre.com,
        mika.westerberg@...ux.intel.com, efremov@...ux.com,
        ztuowen@...il.com, lkml <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH] devres: keep both device name and resource name in pretty name

On Sat, 30 May 2020 at 23:06, Vladimir Oltean <olteanv@...il.com> wrote:
>
> From: Vladimir Oltean <vladimir.oltean@....com>
>
> Some device drivers have many memory regions, and sometimes debugging is
> easiest using devmem on its register map. Take for example a networking
> switch. Its memory map used to look like this in /proc/iomem:
>
> 1fc000000-1fc3fffff : pcie@...000000
>   1fc000000-1fc3fffff : 0000:00:00.5
>     1fc010000-1fc01ffff : sys
>     1fc030000-1fc03ffff : rew
>     1fc060000-1fc0603ff : s2
>     1fc070000-1fc0701ff : devcpu_gcb
>     1fc080000-1fc0800ff : qs
>     1fc090000-1fc0900cb : ptp
>     1fc100000-1fc10ffff : port0
>     1fc110000-1fc11ffff : port1
>     1fc120000-1fc12ffff : port2
>     1fc130000-1fc13ffff : port3
>     1fc140000-1fc14ffff : port4
>     1fc150000-1fc15ffff : port5
>     1fc200000-1fc21ffff : qsys
>     1fc280000-1fc28ffff : ana
>
> But after said patch, the information is now presented in a much more
> opaque way:
>
> 1fc000000-1fc3fffff : pcie@...000000
>   1fc000000-1fc3fffff : 0000:00:00.5
>     1fc010000-1fc01ffff : 0000:00:00.5
>     1fc030000-1fc03ffff : 0000:00:00.5
>     1fc060000-1fc0603ff : 0000:00:00.5
>     1fc070000-1fc0701ff : 0000:00:00.5
>     1fc080000-1fc0800ff : 0000:00:00.5
>     1fc090000-1fc0900cb : 0000:00:00.5
>     1fc100000-1fc10ffff : 0000:00:00.5
>     1fc110000-1fc11ffff : 0000:00:00.5
>     1fc120000-1fc12ffff : 0000:00:00.5
>     1fc130000-1fc13ffff : 0000:00:00.5
>     1fc140000-1fc14ffff : 0000:00:00.5
>     1fc150000-1fc15ffff : 0000:00:00.5
>     1fc200000-1fc21ffff : 0000:00:00.5
>     1fc280000-1fc28ffff : 0000:00:00.5
>
> It is a fair comment that /proc/iomem might be confusing when it shows
> resources without an associated device, but we can do better than just
> hide the resource name altogether. Namely, we can print the device
> name _and_ the resource name. Like this:
>
> 1fc000000-1fc3fffff : pcie@...000000
>   1fc000000-1fc3fffff : 0000:00:00.5
>     1fc010000-1fc01ffff : 0000:00:00.5 sys
>     1fc030000-1fc03ffff : 0000:00:00.5 rew
>     1fc060000-1fc0603ff : 0000:00:00.5 s2
>     1fc070000-1fc0701ff : 0000:00:00.5 devcpu_gcb
>     1fc080000-1fc0800ff : 0000:00:00.5 qs
>     1fc090000-1fc0900cb : 0000:00:00.5 ptp
>     1fc100000-1fc10ffff : 0000:00:00.5 port0
>     1fc110000-1fc11ffff : 0000:00:00.5 port1
>     1fc120000-1fc12ffff : 0000:00:00.5 port2
>     1fc130000-1fc13ffff : 0000:00:00.5 port3
>     1fc140000-1fc14ffff : 0000:00:00.5 port4
>     1fc150000-1fc15ffff : 0000:00:00.5 port5
>     1fc200000-1fc21ffff : 0000:00:00.5 qsys
>     1fc280000-1fc28ffff : 0000:00:00.5 ana
>
> Fixes: 8d84b18f5678 ("devres: always use dev_name() in devm_ioremap_resource()")
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
> ---

I just realized I haven't done any error checking whatsoever on memory
allocation. So let's keep discussing only on the general idea of the
patch, if people are ok with it, I'll send a v2.

>  lib/devres.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/lib/devres.c b/lib/devres.c
> index 6ef51f159c54..25b78b0cb5cc 100644
> --- a/lib/devres.c
> +++ b/lib/devres.c
> @@ -119,6 +119,7 @@ __devm_ioremap_resource(struct device *dev, const struct resource *res,
>  {
>         resource_size_t size;
>         void __iomem *dest_ptr;
> +       char *pretty_name;
>
>         BUG_ON(!dev);
>
> @@ -129,7 +130,16 @@ __devm_ioremap_resource(struct device *dev, const struct resource *res,
>
>         size = resource_size(res);
>
> -       if (!devm_request_mem_region(dev, res->start, size, dev_name(dev))) {
> +       if (res->name) {
> +               int len = strlen(dev_name(dev)) + strlen(res->name) + 2;
> +
> +               pretty_name = devm_kzalloc(dev, len, GFP_KERNEL);
> +               sprintf(pretty_name, "%s %s", dev_name(dev), res->name);
> +       } else {
> +               pretty_name = devm_kstrdup(dev, dev_name(dev), GFP_KERNEL);
> +       }
> +
> +       if (!devm_request_mem_region(dev, res->start, size, pretty_name)) {
>                 dev_err(dev, "can't request region for resource %pR\n", res);
>                 return IOMEM_ERR_PTR(-EBUSY);
>         }
> --
> 2.25.1
>

Thanks,
-Vladimir

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