On Tue, May 26, 2020 at 11:35:02AM +0530, Sanjay R Mehta wrote:
> Apologies for my delayed response.
>
> >> +#include <linux/module.h>
> >> +#include <linux/kernel.h>
> >> +#include <linux/pci.h>
> >> +#include <linux/dma-mapping.h>
> >> +#include <linux/interrupt.h>
> >> +
> >> +#include "ptdma.h"
> >> +
> >> +static int cmd_queue_length = 32;
> >> +module_param(cmd_queue_length, uint, 0644);
> >> +MODULE_PARM_DESC(cmd_queue_length,
> >> + " length of the command queue, a power of 2 (2 <= val <=
> >> 128)");
> >
> > Any reason for this as module param? who will configure this and how?
> >
> The command queue length can be from 2 to 64K command.
> Therefore added as module parameter to allow the length of the queue to be
> specified at load time.
Please no, this is not the 1990's. No one can use them easily, make
this configurable on a per-device basis if you really need to be able to
change this.
But step back, why do you need to change this at all? Why do you have a
limit and why can you not just do this dynamically? The goal here
should not have any user-changable options at all, it should "just
work".
> >> + * List of PTDMAs, PTDMA count, read-write access lock, and access
> >> functions
> >> + *
> >> + * Lock structure: get pt_unit_lock for reading whenever we need to
> >> + * examine the PTDMA list. While holding it for reading we can acquire
> >> + * the RR lock to update the round-robin next-PTDMA pointer. The unit lock
> >> + * must be acquired before the RR lock.
> >> + *
> >> + * If the unit-lock is acquired for writing, we have total control over
> >> + * the list, so there's no value in getting the RR lock.
> >> + */
> >> +static DEFINE_RWLOCK(pt_unit_lock);
> >> +static LIST_HEAD(pt_units);
> >> +
> >> +static struct pt_device *pt_rr;
> >
> > why do we need these globals and not in driver context?
> >
> The AMD SOC has multiple PT controller's with the same PCI device ID and
> hence the same driver is probed for each instance.
> The driver stores the pt_device context of each PT controller in this global
> list.
That's horrid and not needed at all. No driver should have a static
list anymore, again, this isn't the 1990's :)
> >> +static void pt_add_device(struct pt_device *pt)
> >> +{
> >> + unsigned long flags;
> >> +
> >> + write_lock_irqsave(&pt_unit_lock, flags);
> >> + list_add_tail(&pt->entry, &pt_units);
> >> + if (!pt_rr)
> >> + /*
> >> + * We already have the list lock (we're first) so this
> >> + * pointer can't change on us. Set its initial value.
> >> + */
> >> + pt_rr = pt;
> >> + write_unlock_irqrestore(&pt_unit_lock, flags);
> >> +}
> >
> > Can you please explain what do you mean by having a list of devices and
> > why are we adding/removing dynamically?
> >
> Since AMD SOC has many PT controller's with the same PCI device ID and
> hence the same driver probed for initialization of each PT controller device
> instance.
That's fine, PCI drivers should all work on a per-device basis and not
care if there are 1, or 1000 of the same device in the system.
> Also, the number of PT controller varies for different AMD SOC's.
Again, that's fine.
> Therefore the dynamic adding/removing of each PT controller context to global
> device list implemented.
Such a list should never be needed, unless you are doing something
really wrong. Please remove it and use the proper PCI device driver
apis for your individual instances instead.
thanks,
greg k-h
