[PATCH] libertas: remove internal buffers from GSPI driver
Dan Williams
dcbw at redhat.com
Tue Dec 1 03:19:37 EST 2009
On Mon, 2009-11-30 at 16:53 -0800, Colin McCabe wrote:
> On Tue, Oct 27, 2009 at 3:51 PM, Andrey Yurovsky <andrey at cozybit.com> wrote:
> > This patch removes the internal command and data buffers that the GSPI driver
> > maintained and instead relies on the Libertas core to synchronize access
> > to the command and data ports as with the other interface drivers.
>
> Hi all,
>
> I'm glad to see you're improving stuff. Good catch with some of the
> recent bugfixes.
>
> However... it seems like you are headed for a "scheduling while
> atomic" with this patch.
>
> The original reason why if_spi_host_to_card copied the data into a
> buffer, rather than simply calling spu_write and being done with it,
> was that spu_write needed to sleep. spu_write invokes spi_sync, which
> has a big comment that says "This call may only be used from a context
> that may sleep."
>
> Unfortunately, if_spi_host_to_card is called from contexts where we
> hold a spinlock. For example, lbs_main does
>
> spin_lock_irq(&priv->driver_lock);
> if (!priv->dnld_sent && priv->tx_pending_len > 0) {
> int ret = priv->hw_host_to_card(priv, MVMS_DAT,
>
> priv->tx_pending_buf,
>
> priv->tx_pending_len);
> ...etc...
>
> Perhaps the easiest thing would be to get rid of this usage of hw_host_to_card?
> spu_write will always have to busy-wait from time to time because the
> SPU requires a delay between successive transactions. Busy-waiting
> under a spinlock, with interrupts disabled, just doesn't seem right.
I so want to kill dnld_sent. That variable is pretty confusing and I
think it can be architected better. That still leaves tx_pending_len;
the problem there is that we do have a TX queue and we need to protect
it against concurrent access. Incoming packets to TX can be queued at
any time by the upper layers of the network stack.
The fix for this is to make tx_pending_buf a *pointer* to a chunk of
memory in lbs_private, say "u8 tx_buf_real[LBS_UPLD_SIZE]". When there
is no packet to TX, tx_pending_buf points to tx_buf_real[]. Thus
incoming packets to lbs_hard_start_xmit() can be copied into that buffer
immediately, and the buffer is still protected by the lock. When a
packet is currently being TXed, tx_pending_buf would be NULL, and
hard_start_xmit() would return NETDEV_TX_BUSY like it currently does.
When the transmit is triggered, the lock is taken, tx_pending_buf is set
to NULL, the lock is released, and the address tx_buf_real[] is sent to
hw_host_to_card(). Thus hw_host_to_card() doesn't have to be under the
lock anymore, because nothing will be writing to tx_buf_real[].
We need to keep tx_buf_real[] as a statically allocated array so that if
the module is removed during TX, we don't need to kfree() any buffers
(which the TX might be using). Obviously we could just spin until the
TX was done and free the buffer, but it's already statically allocated
and keeping that way is just easier.
At least that's my 10 minute thought... There might be other variables
that hw_host_to_card uses (like dnld_sent) that are protected by the
lock, but dnld_sent (and cur_cmd_retcode) needs to die die die.
Dan
> Also the comment in if_spi_c2h_cmd that "we need a buffer big enough
> to handle whatever people send to hw_host_to_card" should go away if
> the buffer is not used in hw_host_to_card.
>
> > This is an incremental cleanup: after removing the redundant buffers, we
> > can further improve the driver to use a threaded IRQ handler instead of
> > maintaining its own thread. However I would like a few folks to test
> > the buffer removal first and make sure that I'm not introducing
> > regressions.
>
> Threaded IRQs, cool. I'm waiting for that patch. :)
>
> Colin
>
>
> >
> > Tested on Blackfin BF527 with DMA disabled due to an issue with the SPI
> > host controller driver in the current bleeding-edge Blackfin kernel. I
> > would appreciate it if someone with working DMA could test this patch
> > and provide feedback.
> >
> > Signed-off-by: Andrey Yurovsky <andrey at cozybit.com>
> > ---
> > drivers/net/wireless/libertas/if_spi.c | 136 ++------------------------------
> > 1 files changed, 6 insertions(+), 130 deletions(-)
> >
> > diff --git a/drivers/net/wireless/libertas/if_spi.c b/drivers/net/wireless/libertas/if_spi.c
> > index 06df2e1..9e0096d 100644
> > --- a/drivers/net/wireless/libertas/if_spi.c
> > +++ b/drivers/net/wireless/libertas/if_spi.c
> > @@ -32,12 +32,6 @@
> > #include "dev.h"
> > #include "if_spi.h"
> >
> > -struct if_spi_packet {
> > - struct list_head list;
> > - u16 blen;
> > - u8 buffer[0] __attribute__((aligned(4)));
> > -};
> > -
> > struct if_spi_card {
> > struct spi_device *spi;
> > struct lbs_private *priv;
> > @@ -66,33 +60,10 @@ struct if_spi_card {
> > struct semaphore spi_thread_terminated;
> >
> > u8 cmd_buffer[IF_SPI_CMD_BUF_SIZE];
> > -
> > - /* A buffer of incoming packets from libertas core.
> > - * Since we can't sleep in hw_host_to_card, we have to buffer
> > - * them. */
> > - struct list_head cmd_packet_list;
> > - struct list_head data_packet_list;
> > -
> > - /* Protects cmd_packet_list and data_packet_list */
> > - spinlock_t buffer_lock;
> > };
> >
> > static void free_if_spi_card(struct if_spi_card *card)
> > {
> > - struct list_head *cursor, *next;
> > - struct if_spi_packet *packet;
> > -
> > - BUG_ON(card->run_thread);
> > - list_for_each_safe(cursor, next, &card->cmd_packet_list) {
> > - packet = container_of(cursor, struct if_spi_packet, list);
> > - list_del(&packet->list);
> > - kfree(packet);
> > - }
> > - list_for_each_safe(cursor, next, &card->data_packet_list) {
> > - packet = container_of(cursor, struct if_spi_packet, list);
> > - list_del(&packet->list);
> > - kfree(packet);
> > - }
> > spi_set_drvdata(card->spi, NULL);
> > kfree(card);
> > }
> > @@ -774,40 +745,6 @@ out:
> > return err;
> > }
> >
> > -/* Move data or a command from the host to the card. */
> > -static void if_spi_h2c(struct if_spi_card *card,
> > - struct if_spi_packet *packet, int type)
> > -{
> > - int err = 0;
> > - u16 int_type, port_reg;
> > -
> > - switch (type) {
> > - case MVMS_DAT:
> > - int_type = IF_SPI_CIC_TX_DOWNLOAD_OVER;
> > - port_reg = IF_SPI_DATA_RDWRPORT_REG;
> > - break;
> > - case MVMS_CMD:
> > - int_type = IF_SPI_CIC_CMD_DOWNLOAD_OVER;
> > - port_reg = IF_SPI_CMD_RDWRPORT_REG;
> > - break;
> > - default:
> > - lbs_pr_err("can't transfer buffer of type %d\n", type);
> > - err = -EINVAL;
> > - goto out;
> > - }
> > -
> > - /* Write the data to the card */
> > - err = spu_write(card, port_reg, packet->buffer, packet->blen);
> > - if (err)
> > - goto out;
> > -
> > -out:
> > - kfree(packet);
> > -
> > - if (err)
> > - lbs_pr_err("%s: error %d\n", __func__, err);
> > -}
> > -
> > /* Inform the host about a card event */
> > static void if_spi_e2h(struct if_spi_card *card)
> > {
> > @@ -837,8 +774,6 @@ static int lbs_spi_thread(void *data)
> > int err;
> > struct if_spi_card *card = data;
> > u16 hiStatus;
> > - unsigned long flags;
> > - struct if_spi_packet *packet;
> >
> > while (1) {
> > /* Wait to be woken up by one of two things. First, our ISR
> > @@ -877,43 +812,9 @@ static int lbs_spi_thread(void *data)
> > if (hiStatus & IF_SPI_HIST_CMD_DOWNLOAD_RDY ||
> > (card->priv->psstate != PS_STATE_FULL_POWER &&
> > (hiStatus & IF_SPI_HIST_TX_DOWNLOAD_RDY))) {
> > - /* This means two things. First of all,
> > - * if there was a previous command sent, the card has
> > - * successfully received it.
> > - * Secondly, it is now ready to download another
> > - * command.
> > - */
> > lbs_host_to_card_done(card->priv);
> > -
> > - /* Do we have any command packets from the host to
> > - * send? */
> > - packet = NULL;
> > - spin_lock_irqsave(&card->buffer_lock, flags);
> > - if (!list_empty(&card->cmd_packet_list)) {
> > - packet = (struct if_spi_packet *)(card->
> > - cmd_packet_list.next);
> > - list_del(&packet->list);
> > - }
> > - spin_unlock_irqrestore(&card->buffer_lock, flags);
> > -
> > - if (packet)
> > - if_spi_h2c(card, packet, MVMS_CMD);
> > }
> > - if (hiStatus & IF_SPI_HIST_TX_DOWNLOAD_RDY) {
> > - /* Do we have any data packets from the host to
> > - * send? */
> > - packet = NULL;
> > - spin_lock_irqsave(&card->buffer_lock, flags);
> > - if (!list_empty(&card->data_packet_list)) {
> > - packet = (struct if_spi_packet *)(card->
> > - data_packet_list.next);
> > - list_del(&packet->list);
> > - }
> > - spin_unlock_irqrestore(&card->buffer_lock, flags);
> >
> > - if (packet)
> > - if_spi_h2c(card, packet, MVMS_DAT);
> > - }
> > if (hiStatus & IF_SPI_HIST_CARD_EVENT)
> > if_spi_e2h(card);
> >
> > @@ -942,40 +843,18 @@ static int if_spi_host_to_card(struct lbs_private *priv,
> > u8 type, u8 *buf, u16 nb)
> > {
> > int err = 0;
> > - unsigned long flags;
> > struct if_spi_card *card = priv->card;
> > - struct if_spi_packet *packet;
> > - u16 blen;
> >
> > lbs_deb_enter_args(LBS_DEB_SPI, "type %d, bytes %d", type, nb);
> >
> > - if (nb == 0) {
> > - lbs_pr_err("%s: invalid size requested: %d\n", __func__, nb);
> > - err = -EINVAL;
> > - goto out;
> > - }
> > - blen = ALIGN(nb, 4);
> > - packet = kzalloc(sizeof(struct if_spi_packet) + blen, GFP_ATOMIC);
> > - if (!packet) {
> > - err = -ENOMEM;
> > - goto out;
> > - }
> > - packet->blen = blen;
> > - memcpy(packet->buffer, buf, nb);
> > - memset(packet->buffer + nb, 0, blen - nb);
> > + nb = ALIGN(nb, 4);
> >
> > switch (type) {
> > case MVMS_CMD:
> > - priv->dnld_sent = DNLD_CMD_SENT;
> > - spin_lock_irqsave(&card->buffer_lock, flags);
> > - list_add_tail(&packet->list, &card->cmd_packet_list);
> > - spin_unlock_irqrestore(&card->buffer_lock, flags);
> > + err = spu_write(card, IF_SPI_CMD_RDWRPORT_REG, buf, nb);
> > break;
> > case MVMS_DAT:
> > - priv->dnld_sent = DNLD_DATA_SENT;
> > - spin_lock_irqsave(&card->buffer_lock, flags);
> > - list_add_tail(&packet->list, &card->data_packet_list);
> > - spin_unlock_irqrestore(&card->buffer_lock, flags);
> > + err = spu_write(card, IF_SPI_DATA_RDWRPORT_REG, buf, nb);
> > break;
> > default:
> > lbs_pr_err("can't transfer buffer of type %d", type);
> > @@ -983,9 +862,6 @@ static int if_spi_host_to_card(struct lbs_private *priv,
> > break;
> > }
> >
> > - /* Wake up the spi thread */
> > - up(&card->spi_ready);
> > -out:
> > lbs_deb_leave_args(LBS_DEB_SPI, "err=%d", err);
> > return err;
> > }
> > @@ -1062,9 +938,6 @@ static int __devinit if_spi_probe(struct spi_device *spi)
> >
> > sema_init(&card->spi_ready, 0);
> > sema_init(&card->spi_thread_terminated, 0);
> > - INIT_LIST_HEAD(&card->cmd_packet_list);
> > - INIT_LIST_HEAD(&card->data_packet_list);
> > - spin_lock_init(&card->buffer_lock);
> >
> > /* Initialize the SPI Interface Unit */
> > err = spu_init(card, pdata->use_dummy_writes);
> > @@ -1141,6 +1014,9 @@ static int __devinit if_spi_probe(struct spi_device *spi)
> > goto terminate_thread;
> > }
> >
> > + /* poke the IRQ handler so that we don't miss the first interrupt */
> > + up(&card->spi_ready);
> > +
> > /* Start the card.
> > * This will call register_netdev, and we'll start
> > * getting interrupts... */
> > --
> > 1.5.6.3
> >
> >
> > _______________________________________________
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> > libertas-dev at lists.infradead.org
> > http://lists.infradead.org/mailman/listinfo/libertas-dev
> >
>
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