Re: [PATCH v2 1/5] iommu/amd - Add debugfs support

[Gary R Hook]

On 03/13/2018 12:16 PM, Andy Shevchenko wrote:
> On Fri, Mar 9, 2018 at 2:50 AM, Gary R Hook <gary.hook@xxxxxxx> wrote:
>
> > +       default n
>
> Redundant

Roger that.

> > +#include <linux/pci.h>
> > +#include <linux/iommu.h>
> > +#include <linux/debugfs.h>
>
> Keep in order?

What order would that be? These few needed files are listed in the same
order as which they appear in amd_iommu.c. I'm gonna need a preference
spelled out, please (and a rationale, so I may better understand).

> > +#include "amd_iommu_proto.h"
> > +#include "amd_iommu_types.h"
>
> > +/* DebugFS helpers */
> > +#define        OBUFP           (obuf + oboff)
> > +#define        OBUFLEN         obuflen
> > +#define        OBUFSPC         (OBUFLEN - oboff)
> > +#define        OSCNPRINTF(fmt, ...) \
> > +               scnprintf(OBUFP, OBUFSPC, fmt, ## __VA_ARGS__)
>
> I don't see any advantages of this. Other way around, they will simple
> makes things hard to read an understand in place.

I used this technique in the CCP driver code (where it was accepted), in 
an effort to do the opposite of what you claim: make the code more 
readable. Given the 80 column limit, a large number of arguments, and 
very long statements, IMO something needs to give. I don't find the use 
of #defines to be obfuscating.

I'm not trying to argue, but rather simply state the perspective / 
reasoning I used to create a source file I feel is manageable. I have 17 
more iommu patches built upon this strategy, and this seems to be 
advantageous for all of them.

> > +       for (i = start ; i <= end ; i++)
>
> Missed {}

Wasn't sure about the M.O. given that the body of this loop is a single 
if statement. And I don't see anywhere in
https://www.kernel.org/doc/html/latest/process/coding-style.html
in section 3.1 where curly braces are called for in this situation. May 
I ask for clarification on the style rule, please?

> > +               if ((amd_iommu_dev_table[i].data[0] ^ 0x3)
> > +                   || amd_iommu_dev_table[i].data[1])
> > +                       n++;
> > +       return n;
> > +}
>
> > +
> > +static ssize_t amd_iommu_debugfs_dtecount_read(struct file *filp,
> > +                                         char __user *ubuf,
> > +                                         size_t count, loff_t *offp)
> > +{
> > +       struct amd_iommu *iommu = filp->private_data;
>
> > +       unsigned int obuflen = 512;
>
> Sounds like way too much.

I can tune these up.

> > +       if (!iommu)
> > +               return 0;
>
> When this possible?

It was intended as a sanity check, but if this happens, much worse has 
already gone wrong. I'll remove.

> > +       obuf = kmalloc(OBUFLEN, GFP_KERNEL);
> > +       if (!obuf)
> > +               return -ENOMEM;
> > +
> > +       n = amd_iommu_count_valid_dtes(0, 0xFFFF);
> > +       oboff += OSCNPRINTF("%d\n", n);
>
> > +       return ret;
> > +}
>
>
> > @@ -89,6 +89,7 @@
> >   #define ACPI_DEVFLAG_ATSDIS             0x10000000
> >
> >   #define LOOP_TIMEOUT   100000
> > +
> >   /*
> >    * ACPI table definitions
> >    *
>
> Doesn't belong to the patch.

I'm sorry, I don't understand. The added blank line doesn't belong to 
the patch?

> > +#endif
> > +
> > +
>
> Extra unneeded line.
Thanks,