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SubjectRe: [PATCH v7 10/12] powerpc/vas: Define vas_win_close() interface
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Hi Suka,

More comments :)

Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com> writes:

> diff --git a/arch/powerpc/platforms/powernv/vas-window.c b/arch/powerpc/platforms/powernv/vas-window.c
> index 2dd4b63..24288dd 100644
> --- a/arch/powerpc/platforms/powernv/vas-window.c
> +++ b/arch/powerpc/platforms/powernv/vas-window.c
> @@ -879,11 +887,92 @@ struct vas_window *vas_rx_win_open(int vasid, enum vas_cop_type cop,
> }
> EXPORT_SYMBOL_GPL(vas_rx_win_open);
>
> -/* stub for now */
> +static void poll_window_busy_state(struct vas_window *window)
> +{
> + int busy;
> + uint64_t val;
> +
> +retry:
> + /*
> + * Poll Window Busy flag
> + */
> + val = read_hvwc_reg(window, VREG(WIN_STATUS));
> + busy = GET_FIELD(VAS_WIN_BUSY, val);
> + if (busy) {
> + val = 0;
> + schedule_timeout(2000);

What's 2000?

That's in jiffies, so it's not a fixed amount of time.

But on a typical config that will be 20 _seconds_ ?!

But you haven't set the task state, so AFAIK it will just return
instantly.

And if there's a software/hardware bug and it never stops being busy,
then we have a softlockup. The other option would be print a big fat
warning and just not free the window. But maybe that doesn't work for
other reasons.

> + goto retry;
> + }
> +}
> +
> +static void poll_window_castout(struct vas_window *window)
> +{
> + int cached;
> + uint64_t val;
> +
> + /* Cast window context out of the cache */
> +retry:
> + val = read_hvwc_reg(window, VREG(WIN_CTX_CACHING_CTL));
> + cached = GET_FIELD(VAS_WIN_CACHE_STATUS, val);
> + if (cached) {
> + val = 0ULL;
> + val = SET_FIELD(VAS_CASTOUT_REQ, val, 1);
> + val = SET_FIELD(VAS_PUSH_TO_MEM, val, 0);
> + write_hvwc_reg(window, VREG(WIN_CTX_CACHING_CTL), val);

Sigh, I still don't like that macro :)

or:
write_hvwc_reg(window, VREG(WIN_CTX_CACHING_CTL), 1ull << 63);

> +
> + schedule_timeout(2000);
> + goto retry;
> + }
> +}
> +
> +/*
> + * Close a window.
> + *
> + * See Section 1.12.1 of VAS workbook v1.05 for details on closing window:
> + * - Disable new paste operations (unmap paste address)
> + * - Poll for the "Window Busy" bit to be cleared
> + * - Clear the Open/Enable bit for the Window.
> + * - Poll for return of window Credits (implies FIFO empty for Rx win?)
> + * - Unpin and cast window context out of cache
> + *
> + * Besides the hardware, kernel has some bookkeeping of course.
> + */
> int vas_win_close(struct vas_window *window)
> {
> - return -1;
> + uint64_t val;
> +
> + if (!window)
> + return 0;
> +
> + if (!window->tx_win && atomic_read(&window->num_txwins) != 0) {
> + pr_devel("VAS: Attempting to close an active Rx window!\n");
> + WARN_ON_ONCE(1);
> + return -EAGAIN;

EAGAIN means "if you do the same thing again it might work".

I don't think that's right here. The window is not in a state where it
can be freed, the caller needs to do something to fix that.

EBUSY would probably be more appropriate.


cheers

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