Re: [PATCH 2/6] spi: sun4i: restrict transfer length in PIO-mode

[Sergey Suloev]

On 04/03/2018 02:40 PM, Maxime Ripard wrote:

On Tue, Apr 03, 2018 at 02:08:43PM +0300, Sergey Suloev wrote:

On 04/03/2018 11:10 AM, Maxime Ripard wrote:

On Thu, Mar 29, 2018 at 09:59:03PM +0300, Sergey Suloev wrote:

There is no need to handle 3/4 empty/full interrupts as the maximum
supported transfer length in PIO mode is 64 bytes for sun4i-family
SoCs.

That assumes that you'll be able to treat the FIFO full interrupt and
drain the FIFO before we have the next byte coming in. This would
require a real time system, and we're not in one of them.

AFAIK in SPI protocol we send and receive at the same time.

It depends. The protocol allows it yes, but most devices I've seen can
only operate in half duplex. But it's not really the point.


As soon as the transfer length is <= FIFO depth then it means that
at the moment we get TC interrupt all data for this transfer
sent/received already.

Is your point here that draining FIFO might be a long operation and we can
lose next portion of data ?

My point is that, if you get another interrupt(s) right before the
FIFO full interrupt, that interrupt is going to be masked for as long
as it is needed for the previous handler(s) to execute.

If you're having another byte received while the interrupt is masked,
you're losing data.

Maxime



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ok, I am going to put back 3/4 full handler then.

Re: [PATCH 2/6] spi: sun4i: restrict transfer length in PIO-mode

[Sergey Suloev]

On 04/03/2018 02:40 PM, Maxime Ripard wrote:

On Tue, Apr 03, 2018 at 02:08:43PM +0300, Sergey Suloev wrote:

On 04/03/2018 11:10 AM, Maxime Ripard wrote:

On Thu, Mar 29, 2018 at 09:59:03PM +0300, Sergey Suloev wrote:

There is no need to handle 3/4 empty/full interrupts as the maximum
supported transfer length in PIO mode is 64 bytes for sun4i-family
SoCs.

That assumes that you'll be able to treat the FIFO full interrupt and
drain the FIFO before we have the next byte coming in. This would
require a real time system, and we're not in one of them.

AFAIK in SPI protocol we send and receive at the same time.

It depends. The protocol allows it yes, but most devices I've seen can
only operate in half duplex. But it's not really the point.


As soon as the transfer length is <= FIFO depth then it means that
at the moment we get TC interrupt all data for this transfer
sent/received already.

Is your point here that draining FIFO might be a long operation and we can
lose next portion of data ?

My point is that, if you get another interrupt(s) right before the
FIFO full interrupt, that interrupt is going to be masked for as long
as it is needed for the previous handler(s) to execute.

If you're having another byte received while the interrupt is masked,
you're losing data.

Maxime



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ok, I am going to put back 3/4 full handler then.

Re: [PATCH 2/6] spi: sun4i: restrict transfer length in PIO-mode

[Maxime Ripard]

On Tue, Apr 03, 2018 at 02:08:43PM +0300, Sergey Suloev wrote:
> On 04/03/2018 11:10 AM, Maxime Ripard wrote:
> > On Thu, Mar 29, 2018 at 09:59:03PM +0300, Sergey Suloev wrote:
> > > There is no need to handle 3/4 empty/full interrupts as the maximum
> > > supported transfer length in PIO mode is 64 bytes for sun4i-family
> > > SoCs.
> > That assumes that you'll be able to treat the FIFO full interrupt and
> > drain the FIFO before we have the next byte coming in. This would
> > require a real time system, and we're not in one of them.
>
> AFAIK in SPI protocol we send and receive at the same time.

It depends. The protocol allows it yes, but most devices I've seen can
only operate in half duplex. But it's not really the point.

> As soon as the transfer length is <= FIFO depth then it means that
> at the moment we get TC interrupt all data for this transfer
> sent/received already.
> 
> Is your point here that draining FIFO might be a long operation and we can
> lose next portion of data ?

My point is that, if you get another interrupt(s) right before the
FIFO full interrupt, that interrupt is going to be masked for as long
as it is needed for the previous handler(s) to execute.

If you're having another byte received while the interrupt is masked,
you're losing data.

Maxime

-- 
Maxime Ripard, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com


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Re: [PATCH 2/6] spi: sun4i: restrict transfer length in PIO-mode

[Maxime Ripard]

On Tue, Apr 03, 2018 at 02:08:43PM +0300, Sergey Suloev wrote:
> On 04/03/2018 11:10 AM, Maxime Ripard wrote:
> > On Thu, Mar 29, 2018 at 09:59:03PM +0300, Sergey Suloev wrote:
> > > There is no need to handle 3/4 empty/full interrupts as the maximum
> > > supported transfer length in PIO mode is 64 bytes for sun4i-family
> > > SoCs.
> > That assumes that you'll be able to treat the FIFO full interrupt and
> > drain the FIFO before we have the next byte coming in. This would
> > require a real time system, and we're not in one of them.
>
> AFAIK in SPI protocol we send and receive at the same time.

It depends. The protocol allows it yes, but most devices I've seen can
only operate in half duplex. But it's not really the point.

> As soon as the transfer length is <= FIFO depth then it means that
> at the moment we get TC interrupt all data for this transfer
> sent/received already.
> 
> Is your point here that draining FIFO might be a long operation and we can
> lose next portion of data ?

My point is that, if you get another interrupt(s) right before the
FIFO full interrupt, that interrupt is going to be masked for as long
as it is needed for the previous handler(s) to execute.

If you're having another byte received while the interrupt is masked,
you're losing data.

Maxime

-- 
Maxime Ripard, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com


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Re: [PATCH 2/6] spi: sun4i: restrict transfer length in PIO-mode

[Sergey Suloev]

On 04/03/2018 11:10 AM, Maxime Ripard wrote:

On Thu, Mar 29, 2018 at 09:59:03PM +0300, Sergey Suloev wrote:

There is no need to handle 3/4 empty/full interrupts as the maximum
supported transfer length in PIO mode is 64 bytes for sun4i-family
SoCs.

That assumes that you'll be able to treat the FIFO full interrupt and
drain the FIFO before we have the next byte coming in. This would
require a real time system, and we're not in one of them.

Maxime

AFAIK in SPI protocol we send and receive at the same time. As soon as 
the transfer length


is <= FIFO depth then it means that at the moment we get TC interrupt 
all data for this transfer


sent/received already.

Is your point here that draining FIFO might be a long operation and we 
can lose next portion of data ?

Re: [PATCH 2/6] spi: sun4i: restrict transfer length in PIO-mode

[Sergey Suloev]

On 04/03/2018 11:10 AM, Maxime Ripard wrote:

On Thu, Mar 29, 2018 at 09:59:03PM +0300, Sergey Suloev wrote:

There is no need to handle 3/4 empty/full interrupts as the maximum
supported transfer length in PIO mode is 64 bytes for sun4i-family
SoCs.

That assumes that you'll be able to treat the FIFO full interrupt and
drain the FIFO before we have the next byte coming in. This would
require a real time system, and we're not in one of them.

Maxime

AFAIK in SPI protocol we send and receive at the same time. As soon as 
the transfer length


is <= FIFO depth then it means that at the moment we get TC interrupt 
all data for this transfer


sent/received already.

Is your point here that draining FIFO might be a long operation and we 
can lose next portion of data ?

Re: [PATCH 2/6] spi: sun4i: restrict transfer length in PIO-mode

[Sergey Suloev]

On 04/03/2018 11:10 AM, Maxime Ripard wrote:

On Thu, Mar 29, 2018 at 09:59:03PM +0300, Sergey Suloev wrote:

There is no need to handle 3/4 empty/full interrupts as the maximum
supported transfer length in PIO mode is 64 bytes for sun4i-family
SoCs.

That assumes that you'll be able to treat the FIFO full interrupt and
drain the FIFO before we have the next byte coming in. This would
require a real time system, and we're not in one of them.

Maxime



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so you think we should still handle 3/4 FIFO full ?

Re: [PATCH 2/6] spi: sun4i: restrict transfer length in PIO-mode

[Sergey Suloev]

On 04/03/2018 11:10 AM, Maxime Ripard wrote:

On Thu, Mar 29, 2018 at 09:59:03PM +0300, Sergey Suloev wrote:

There is no need to handle 3/4 empty/full interrupts as the maximum
supported transfer length in PIO mode is 64 bytes for sun4i-family
SoCs.

That assumes that you'll be able to treat the FIFO full interrupt and
drain the FIFO before we have the next byte coming in. This would
require a real time system, and we're not in one of them.

Maxime



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so you think we should still handle 3/4 FIFO full ?

Re: [PATCH 2/6] spi: sun4i: restrict transfer length in PIO-mode

[Maxime Ripard]

On Thu, Mar 29, 2018 at 09:59:03PM +0300, Sergey Suloev wrote:
> There is no need to handle 3/4 empty/full interrupts as the maximum
> supported transfer length in PIO mode is 64 bytes for sun4i-family
> SoCs.

That assumes that you'll be able to treat the FIFO full interrupt and
drain the FIFO before we have the next byte coming in. This would
require a real time system, and we're not in one of them.

Maxime

-- 
Maxime Ripard, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com


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Re: [PATCH 2/6] spi: sun4i: restrict transfer length in PIO-mode

[Maxime Ripard]

On Thu, Mar 29, 2018 at 09:59:03PM +0300, Sergey Suloev wrote:
> There is no need to handle 3/4 empty/full interrupts as the maximum
> supported transfer length in PIO mode is 64 bytes for sun4i-family
> SoCs.

That assumes that you'll be able to treat the FIFO full interrupt and
drain the FIFO before we have the next byte coming in. This would
require a real time system, and we're not in one of them.

Maxime

-- 
Maxime Ripard, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com


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[PATCH 2/6] spi: sun4i: restrict transfer length in PIO-mode

[Sergey Suloev]

There is no need to handle 3/4 empty/full interrupts
as the maximum supported transfer length in PIO mode
is 64 bytes for sun4i-family SoCs. As long as a
problem was reported previously with filling FIFO
on A10s then we stick with 63 bytes depth.

Signed-off-by: Sergey Suloev 

---
 drivers/spi/spi-sun4i.c | 50 -
 1 file changed, 12 insertions(+), 38 deletions(-)

diff --git a/drivers/spi/spi-sun4i.c b/drivers/spi/spi-sun4i.c
index 4141003..2a49c22 100644
--- a/drivers/spi/spi-sun4i.c
+++ b/drivers/spi/spi-sun4i.c
@@ -22,7 +22,12 @@
 
 #include 
 
-#define SUN4I_FIFO_DEPTH   64
+/*
+ * FIFO length is 64 bytes
+ * But filling the FIFO fully might cause a timeout
+ * on some devices, for example on spi2 on A10s
+ */
+#define SUN4I_FIFO_DEPTH   63
 
 #define SUN4I_RXDATA_REG   0x00
 
@@ -202,7 +207,7 @@ static void sun4i_spi_set_cs(struct spi_device *spi, bool 
enable)
 
 static size_t sun4i_spi_max_transfer_size(struct spi_device *spi)
 {
-   return SUN4I_FIFO_DEPTH - 1;
+   return SUN4I_FIFO_DEPTH;
 }
 
 static int sun4i_spi_transfer_one(struct spi_master *master,
@@ -216,11 +221,8 @@ static int sun4i_spi_transfer_one(struct spi_master 
*master,
int ret = 0;
u32 reg;
 
-   /* We don't support transfer larger than the FIFO */
-   if (tfr->len > SUN4I_MAX_XFER_SIZE)
-   return -EMSGSIZE;
-
-   if (tfr->tx_buf && tfr->len >= SUN4I_MAX_XFER_SIZE)
+   /* We don't support transfers larger than FIFO depth */
+   if (tfr->len > SUN4I_FIFO_DEPTH)
return -EMSGSIZE;
 
reinit_completion(>done);
@@ -313,17 +315,11 @@ static int sun4i_spi_transfer_one(struct spi_master 
*master,
 
/*
 * Fill the TX FIFO
-* Filling the FIFO fully causes timeout for some reason
-* at least on spi2 on A10s
 */
-   sun4i_spi_fill_fifo(sspi, SUN4I_FIFO_DEPTH - 1);
+   sun4i_spi_fill_fifo(sspi, SUN4I_FIFO_DEPTH);
 
-   /* Enable the interrupts */
-   sun4i_spi_enable_interrupt(sspi, SUN4I_INT_CTL_TC |
-SUN4I_INT_CTL_RF_F34);
-   /* Only enable Tx FIFO interrupt if we really need it */
-   if (tx_len > SUN4I_FIFO_DEPTH)
-   sun4i_spi_enable_interrupt(sspi, SUN4I_INT_CTL_TF_E34);
+   /* Enable the transfer complete interrupt */
+   sun4i_spi_enable_interrupt(sspi, SUN4I_INT_CTL_TC);
 
/* Start the transfer */
reg = sun4i_spi_read(sspi, SUN4I_CTL_REG);
@@ -363,28 +359,6 @@ static irqreturn_t sun4i_spi_handler(int irq, void *dev_id)
return IRQ_HANDLED;
}
 
-   /* Receive FIFO 3/4 full */
-   if (status & SUN4I_INT_CTL_RF_F34) {
-   sun4i_spi_drain_fifo(sspi, SUN4I_FIFO_DEPTH);
-   /* Only clear the interrupt _after_ draining the FIFO */
-   sun4i_spi_write(sspi, SUN4I_INT_STA_REG, SUN4I_INT_CTL_RF_F34);
-   return IRQ_HANDLED;
-   }
-
-   /* Transmit FIFO 3/4 empty */
-   if (status & SUN4I_INT_CTL_TF_E34) {
-   sun4i_spi_fill_fifo(sspi, SUN4I_FIFO_DEPTH);
-
-   if (!sspi->len)
-   /* nothing left to transmit */
-   sun4i_spi_disable_interrupt(sspi, SUN4I_INT_CTL_TF_E34);
-
-   /* Only clear the interrupt _after_ re-seeding the FIFO */
-   sun4i_spi_write(sspi, SUN4I_INT_STA_REG, SUN4I_INT_CTL_TF_E34);
-
-   return IRQ_HANDLED;
-   }
-
return IRQ_NONE;
 }
 
-- 
2.16.2

[PATCH 2/6] spi: sun4i: restrict transfer length in PIO-mode

[Sergey Suloev]

There is no need to handle 3/4 empty/full interrupts
as the maximum supported transfer length in PIO mode
is 64 bytes for sun4i-family SoCs. As long as a
problem was reported previously with filling FIFO
on A10s then we stick with 63 bytes depth.

Signed-off-by: Sergey Suloev 

---
 drivers/spi/spi-sun4i.c | 50 -
 1 file changed, 12 insertions(+), 38 deletions(-)

diff --git a/drivers/spi/spi-sun4i.c b/drivers/spi/spi-sun4i.c
index 4141003..2a49c22 100644
--- a/drivers/spi/spi-sun4i.c
+++ b/drivers/spi/spi-sun4i.c
@@ -22,7 +22,12 @@
 
 #include 
 
-#define SUN4I_FIFO_DEPTH   64
+/*
+ * FIFO length is 64 bytes
+ * But filling the FIFO fully might cause a timeout
+ * on some devices, for example on spi2 on A10s
+ */
+#define SUN4I_FIFO_DEPTH   63
 
 #define SUN4I_RXDATA_REG   0x00
 
@@ -202,7 +207,7 @@ static void sun4i_spi_set_cs(struct spi_device *spi, bool 
enable)
 
 static size_t sun4i_spi_max_transfer_size(struct spi_device *spi)
 {
-   return SUN4I_FIFO_DEPTH - 1;
+   return SUN4I_FIFO_DEPTH;
 }
 
 static int sun4i_spi_transfer_one(struct spi_master *master,
@@ -216,11 +221,8 @@ static int sun4i_spi_transfer_one(struct spi_master 
*master,
int ret = 0;
u32 reg;
 
-   /* We don't support transfer larger than the FIFO */
-   if (tfr->len > SUN4I_MAX_XFER_SIZE)
-   return -EMSGSIZE;
-
-   if (tfr->tx_buf && tfr->len >= SUN4I_MAX_XFER_SIZE)
+   /* We don't support transfers larger than FIFO depth */
+   if (tfr->len > SUN4I_FIFO_DEPTH)
return -EMSGSIZE;
 
reinit_completion(>done);
@@ -313,17 +315,11 @@ static int sun4i_spi_transfer_one(struct spi_master 
*master,
 
/*
 * Fill the TX FIFO
-* Filling the FIFO fully causes timeout for some reason
-* at least on spi2 on A10s
 */
-   sun4i_spi_fill_fifo(sspi, SUN4I_FIFO_DEPTH - 1);
+   sun4i_spi_fill_fifo(sspi, SUN4I_FIFO_DEPTH);
 
-   /* Enable the interrupts */
-   sun4i_spi_enable_interrupt(sspi, SUN4I_INT_CTL_TC |
-SUN4I_INT_CTL_RF_F34);
-   /* Only enable Tx FIFO interrupt if we really need it */
-   if (tx_len > SUN4I_FIFO_DEPTH)
-   sun4i_spi_enable_interrupt(sspi, SUN4I_INT_CTL_TF_E34);
+   /* Enable the transfer complete interrupt */
+   sun4i_spi_enable_interrupt(sspi, SUN4I_INT_CTL_TC);
 
/* Start the transfer */
reg = sun4i_spi_read(sspi, SUN4I_CTL_REG);
@@ -363,28 +359,6 @@ static irqreturn_t sun4i_spi_handler(int irq, void *dev_id)
return IRQ_HANDLED;
}
 
-   /* Receive FIFO 3/4 full */
-   if (status & SUN4I_INT_CTL_RF_F34) {
-   sun4i_spi_drain_fifo(sspi, SUN4I_FIFO_DEPTH);
-   /* Only clear the interrupt _after_ draining the FIFO */
-   sun4i_spi_write(sspi, SUN4I_INT_STA_REG, SUN4I_INT_CTL_RF_F34);
-   return IRQ_HANDLED;
-   }
-
-   /* Transmit FIFO 3/4 empty */
-   if (status & SUN4I_INT_CTL_TF_E34) {
-   sun4i_spi_fill_fifo(sspi, SUN4I_FIFO_DEPTH);
-
-   if (!sspi->len)
-   /* nothing left to transmit */
-   sun4i_spi_disable_interrupt(sspi, SUN4I_INT_CTL_TF_E34);
-
-   /* Only clear the interrupt _after_ re-seeding the FIFO */
-   sun4i_spi_write(sspi, SUN4I_INT_STA_REG, SUN4I_INT_CTL_TF_E34);
-
-   return IRQ_HANDLED;
-   }
-
return IRQ_NONE;
 }
 
-- 
2.16.2