[PATCH] net: ethernet: pcnet32: Setup the SRAM and NOUFLO on Am79C97{3,5}

[PATCH] net: ethernet: pcnet32: Setup the SRAM and NOUFLO on Am79C97{3,5}

[Markos Chandras]

On a MIPS Malta board, tons of fifo underflow errors have been observed
when using u-boot as bootloader instead of YAMON. The reason for that
is that YAMON used to set the pcnet device to SRAM mode but u-boot does
not. As a result, the default Tx threshold (64 bytes) is now too small to
keep the fifo relatively used and it can result to Tx fifo underflow errors.
As a result of which, it's best to setup the SRAM on supported controllers
so we can always use the NOUFLO bit.

Cc: <netdev@vger.kernel.org>
Cc: <stable@vger.kernel.org>
Cc: <linux-kernel@vger.kernel.org>
Cc: Don Fry <pcnet32@frontier.com>
Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
---
 drivers/net/ethernet/amd/pcnet32.c | 31 +++++++++++++++++++++++++++++--
 1 file changed, 29 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/amd/pcnet32.c b/drivers/net/ethernet/amd/pcnet32.c
index 11d6e6561df1..7fb099f0c631 100644
--- a/drivers/net/ethernet/amd/pcnet32.c
+++ b/drivers/net/ethernet/amd/pcnet32.c
@@ -1543,7 +1543,7 @@ pcnet32_probe1(unsigned long ioaddr, int shared, struct pci_dev *pdev)
 {
 	struct pcnet32_private *lp;
 	int i, media;
-	int fdx, mii, fset, dxsuflo;
+	int fdx, mii, fset, dxsuflo, sram;
 	int chip_version;
 	char *chipname;
 	struct net_device *dev;
@@ -1580,7 +1580,7 @@ pcnet32_probe1(unsigned long ioaddr, int shared, struct pci_dev *pdev)
 	}
 
 	/* initialize variables */
-	fdx = mii = fset = dxsuflo = 0;
+	fdx = mii = fset = dxsuflo = sram = 0;
 	chip_version = (chip_version >> 12) & 0xffff;
 
 	switch (chip_version) {
@@ -1613,6 +1613,7 @@ pcnet32_probe1(unsigned long ioaddr, int shared, struct pci_dev *pdev)
 		chipname = "PCnet/FAST III 79C973";	/* PCI */
 		fdx = 1;
 		mii = 1;
+		sram = 1;
 		break;
 	case 0x2626:
 		chipname = "PCnet/Home 79C978";	/* PCI */
@@ -1636,6 +1637,7 @@ pcnet32_probe1(unsigned long ioaddr, int shared, struct pci_dev *pdev)
 		chipname = "PCnet/FAST III 79C975";	/* PCI */
 		fdx = 1;
 		mii = 1;
+		sram = 1;
 		break;
 	case 0x2628:
 		chipname = "PCnet/PRO 79C976";
@@ -1664,6 +1666,31 @@ pcnet32_probe1(unsigned long ioaddr, int shared, struct pci_dev *pdev)
 		dxsuflo = 1;
 	}
 
+	/*
+	 * The Am79C973/Am79C975 controllers come with 12K of SRAM
+	 * which we can use for the Tx/Rx buffers but most importantly,
+	 * the use of SRAM allow us to use the BCR18:NOUFLO bit to avoid
+	 * Tx fifo underflows.
+	 */
+	if (sram) {
+		/*
+		 * The SRAM is being configured in two steps. First we
+		 * set the SRAM size in the BCR25:SRAM_SIZE bits. According
+		 * to the datasheet, each bit corresponds to a 512-byte
+		 * page so we can have at most 24 pages. The SRAM_SIZE
+		 * corresponds holds the value of the upper 8 bits of
+		 * the 16-bit SRAM size. The low 8-bits start at 0x00
+		 * and end at 0xff. So the address range is from 0x0000
+		 * up to 0x17ff. Therefore, the SRAM_SIZE is set to 0x17.
+		 * The next step is to set the BCR24:SRAM_BND midway through
+		 * so the Tx and Rx buffers can share the SRAM equally.
+		 */
+		a->write_bcr(ioaddr, 25, 0x17);
+		a->write_bcr(ioaddr, 26, 0xc);
+		/* And finally enable the NOUFLO bit */
+		a->write_bcr(ioaddr, 18, a->read_bcr(ioaddr, 18) | (1 << 11));
+	}
+
 	dev = alloc_etherdev(sizeof(*lp));
 	if (!dev) {
 		ret = -ENOMEM;
-- 
2.3.3

Re: [PATCH] net: ethernet: pcnet32: Setup the SRAM and NOUFLO on Am79C97{3,5}

[Don Fry]

One little change to the comment is needed.  See below

Don

On Wed, 2015-03-18 at 20:10 +0000, Markos Chandras wrote:
> On a MIPS Malta board, tons of fifo underflow errors have been observed
> when using u-boot as bootloader instead of YAMON. The reason for that
> is that YAMON used to set the pcnet device to SRAM mode but u-boot does
> not. As a result, the default Tx threshold (64 bytes) is now too small to
> keep the fifo relatively used and it can result to Tx fifo underflow errors.
> As a result of which, it's best to setup the SRAM on supported controllers
> so we can always use the NOUFLO bit.

> +	/*
> +	 * The Am79C973/Am79C975 controllers come with 12K of SRAM
> +	 * which we can use for the Tx/Rx buffers but most importantly,
> +	 * the use of SRAM allow us to use the BCR18:NOUFLO bit to avoid
> +	 * Tx fifo underflows.
> +	 */
> +	if (sram) {
> +		/*
> +		 * The SRAM is being configured in two steps. First we
> +		 * set the SRAM size in the BCR25:SRAM_SIZE bits. According
> +		 * to the datasheet, each bit corresponds to a 512-byte
> +		 * page so we can have at most 24 pages. The SRAM_SIZE
> +		 * corresponds holds the value of the upper 8 bits of
> +		 * the 16-bit SRAM size. The low 8-bits start at 0x00
> +		 * and end at 0xff. So the address range is from 0x0000
> +		 * up to 0x17ff. Therefore, the SRAM_SIZE is set to 0x17.
> +		 * The next step is to set the BCR24:SRAM_BND midway through
> +		 * so the Tx and Rx buffers can share the SRAM equally.
> +		 */

The comment specifies BCR24 but the code is changing BCR26 which matches
the documentation.  Please correct the comment to avoid confusion.

> +		a->write_bcr(ioaddr, 25, 0x17);
> +		a->write_bcr(ioaddr, 26, 0xc);
> +		/* And finally enable the NOUFLO bit */

Re: [PATCH] net: ethernet: pcnet32: Setup the SRAM and NOUFLO on Am79C97{3,5}

[Markos Chandras]

Hi Don,

On Wed, Mar 18, 2015 at 07:07:34PM -0700, Don Fry wrote:
> One little change to the comment is needed.  See below
> 
> Don
> 
> On Wed, 2015-03-18 at 20:10 +0000, Markos Chandras wrote:
> > +	if (sram) {
> > +		/*
> > +		 * The SRAM is being configured in two steps. First we
> > +		 * set the SRAM size in the BCR25:SRAM_SIZE bits. According
> > +		 * to the datasheet, each bit corresponds to a 512-byte
> > +		 * page so we can have at most 24 pages. The SRAM_SIZE
> > +		 * corresponds holds the value of the upper 8 bits of
> > +		 * the 16-bit SRAM size. The low 8-bits start at 0x00
> > +		 * and end at 0xff. So the address range is from 0x0000
> > +		 * up to 0x17ff. Therefore, the SRAM_SIZE is set to 0x17.
> > +		 * The next step is to set the BCR24:SRAM_BND midway through
> > +		 * so the Tx and Rx buffers can share the SRAM equally.
> > +		 */
> 
> The comment specifies BCR24 but the code is changing BCR26 which matches
> the documentation.  Please correct the comment to avoid confusion.
> 

Ah good catch. I will fix it and send a v2.

-- 
markos

[PATCH v2] net: ethernet: pcnet32: Setup the SRAM and NOUFLO on Am79C97{3,5}

[Markos Chandras]

On a MIPS Malta board, tons of fifo underflow errors have been observed
when using u-boot as bootloader instead of YAMON. The reason for that
is that YAMON used to set the pcnet device to SRAM mode but u-boot does
not. As a result, the default Tx threshold (64 bytes) is now too small to
keep the fifo relatively used and it can result to Tx fifo underflow errors.
As a result of which, it's best to setup the SRAM on supported controllers
so we can always use the NOUFLO bit.

Cc: <netdev@vger.kernel.org>
Cc: <stable@vger.kernel.org>
Cc: <linux-kernel@vger.kernel.org>
Cc: Don Fry <pcnet32@frontier.com>
Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
---
Changes since v1:
- Fix comment
---
 drivers/net/ethernet/amd/pcnet32.c | 31 +++++++++++++++++++++++++++++--
 1 file changed, 29 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/amd/pcnet32.c b/drivers/net/ethernet/amd/pcnet32.c
index 11d6e6561df1..15a8190a6f75 100644
--- a/drivers/net/ethernet/amd/pcnet32.c
+++ b/drivers/net/ethernet/amd/pcnet32.c
@@ -1543,7 +1543,7 @@ pcnet32_probe1(unsigned long ioaddr, int shared, struct pci_dev *pdev)
 {
 	struct pcnet32_private *lp;
 	int i, media;
-	int fdx, mii, fset, dxsuflo;
+	int fdx, mii, fset, dxsuflo, sram;
 	int chip_version;
 	char *chipname;
 	struct net_device *dev;
@@ -1580,7 +1580,7 @@ pcnet32_probe1(unsigned long ioaddr, int shared, struct pci_dev *pdev)
 	}
 
 	/* initialize variables */
-	fdx = mii = fset = dxsuflo = 0;
+	fdx = mii = fset = dxsuflo = sram = 0;
 	chip_version = (chip_version >> 12) & 0xffff;
 
 	switch (chip_version) {
@@ -1613,6 +1613,7 @@ pcnet32_probe1(unsigned long ioaddr, int shared, struct pci_dev *pdev)
 		chipname = "PCnet/FAST III 79C973";	/* PCI */
 		fdx = 1;
 		mii = 1;
+		sram = 1;
 		break;
 	case 0x2626:
 		chipname = "PCnet/Home 79C978";	/* PCI */
@@ -1636,6 +1637,7 @@ pcnet32_probe1(unsigned long ioaddr, int shared, struct pci_dev *pdev)
 		chipname = "PCnet/FAST III 79C975";	/* PCI */
 		fdx = 1;
 		mii = 1;
+		sram = 1;
 		break;
 	case 0x2628:
 		chipname = "PCnet/PRO 79C976";
@@ -1664,6 +1666,31 @@ pcnet32_probe1(unsigned long ioaddr, int shared, struct pci_dev *pdev)
 		dxsuflo = 1;
 	}
 
+	/*
+	 * The Am79C973/Am79C975 controllers come with 12K of SRAM
+	 * which we can use for the Tx/Rx buffers but most importantly,
+	 * the use of SRAM allow us to use the BCR18:NOUFLO bit to avoid
+	 * Tx fifo underflows.
+	 */
+	if (sram) {
+		/*
+		 * The SRAM is being configured in two steps. First we
+		 * set the SRAM size in the BCR25:SRAM_SIZE bits. According
+		 * to the datasheet, each bit corresponds to a 512-byte
+		 * page so we can have at most 24 pages. The SRAM_SIZE
+		 * holds the value of the upper 8 bits of the 16-bit SRAM size.
+		 * The low 8-bits start at 0x00 and end at 0xff. So the
+		 * address range is from 0x0000 up to 0x17ff. Therefore,
+		 * the SRAM_SIZE is set to 0x17. The next step is to set
+		 * the BCR26:SRAM_BND midway through so the Tx and Rx
+		 * buffers can share the SRAM equally.
+		 */
+		a->write_bcr(ioaddr, 25, 0x17);
+		a->write_bcr(ioaddr, 26, 0xc);
+		/* And finally enable the NOUFLO bit */
+		a->write_bcr(ioaddr, 18, a->read_bcr(ioaddr, 18) | (1 << 11));
+	}
+
 	dev = alloc_etherdev(sizeof(*lp));
 	if (!dev) {
 		ret = -ENOMEM;
-- 
2.3.3

Re: [PATCH v2] net: ethernet: pcnet32: Setup the SRAM and NOUFLO on Am79C97{3,5}

[David Miller]

From: Markos Chandras <markos.chandras@imgtec.com>
Date: Thu, 19 Mar 2015 10:28:14 +0000

> On a MIPS Malta board, tons of fifo underflow errors have been observed
> when using u-boot as bootloader instead of YAMON. The reason for that
> is that YAMON used to set the pcnet device to SRAM mode but u-boot does
> not. As a result, the default Tx threshold (64 bytes) is now too small to
> keep the fifo relatively used and it can result to Tx fifo underflow errors.
> As a result of which, it's best to setup the SRAM on supported controllers
> so we can always use the NOUFLO bit.
> 
> Cc: <netdev@vger.kernel.org>
> Cc: <stable@vger.kernel.org>
> Cc: <linux-kernel@vger.kernel.org>
> Cc: Don Fry <pcnet32@frontier.com>
> Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>

Applied.