[v1] 8250: microchip: pci1xxxx: Add PCIe Hot reset disable support for Rev C0 and later devices

[PATCH v1 tty-next] 8250: microchip: pci1xxxx: Add PCIe Hot reset disable support for Rev C0 and later devices

Posted by Rengarajan S 9 months, 3 weeks ago

Systems that issue PCIe hot reset requests during a suspend/resume
cycle cause PCI1XXXX device revisions prior to C0 to get its UART
configuration registers reset to hardware default values. This results
in device inaccessibility and data transfer failures. Starting with
Revision C0, support was added in the device hardware (via the Hot
Reset Disable Bit) to allow resetting only the PCIe interface and its
associated logic, but preserving the UART configuration during a hot
reset. This patch enables the hot reset disable feature during suspend/
resume for C0 and later revisions of the device.

Signed-off-by: Rengarajan S <rengarajan.s@microchip.com>
---
 drivers/tty/serial/8250/8250_pci1xxxx.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_pci1xxxx.c b/drivers/tty/serial/8250/8250_pci1xxxx.c
index e9c51d4e447d..ec573327590f 100644
--- a/drivers/tty/serial/8250/8250_pci1xxxx.c
+++ b/drivers/tty/serial/8250/8250_pci1xxxx.c
@@ -115,6 +115,7 @@
 
 #define UART_RESET_REG				0x94
 #define UART_RESET_D3_RESET_DISABLE		BIT(16)
+#define UART_RESET_HOT_RESET_DISABLE            BIT(17)
 
 #define UART_BURST_STATUS_REG			0x9C
 #define UART_TX_BURST_FIFO			0xA0
@@ -620,7 +621,13 @@ static int pci1xxxx_suspend(struct device *dev)
 	}
 
 	data = readl(p + UART_RESET_REG);
-	writel(data | UART_RESET_D3_RESET_DISABLE, p + UART_RESET_REG);
+
+	if (priv->dev_rev >= 0xC0)
+		writel(data | (UART_RESET_D3_RESET_DISABLE |
+		       UART_RESET_HOT_RESET_DISABLE), p + UART_RESET_REG);
+	else
+		writel(data | UART_RESET_D3_RESET_DISABLE,
+		       p + UART_RESET_REG);
 
 	if (wakeup)
 		writeb(UART_PCI_CTRL_D3_CLK_ENABLE, p + UART_PCI_CTRL_REG);
@@ -647,7 +654,14 @@ static int pci1xxxx_resume(struct device *dev)
 	}
 
 	data = readl(p + UART_RESET_REG);
-	writel(data & ~UART_RESET_D3_RESET_DISABLE, p + UART_RESET_REG);
+
+	if (priv->dev_rev >= 0xC0)
+		writel(data & ~(UART_RESET_D3_RESET_DISABLE |
+		       UART_RESET_HOT_RESET_DISABLE), p + UART_RESET_REG);
+	else
+		writel(data & ~UART_RESET_D3_RESET_DISABLE,
+		       p + UART_RESET_REG);
+
 	iounmap(p);
 
 	for (i = 0; i < priv->nr; i++) {
-- 
2.25.1

Re: [PATCH v1 tty-next] 8250: microchip: pci1xxxx: Add PCIe Hot reset disable support for Rev C0 and later devices

Posted by Jiri Slaby 9 months, 3 weeks ago

On 23. 04. 25, 5:38, Rengarajan S wrote:
> Systems that issue PCIe hot reset requests during a suspend/resume
> cycle cause PCI1XXXX device revisions prior to C0 to get its UART
> configuration registers reset to hardware default values. This results
> in device inaccessibility and data transfer failures. Starting with
> Revision C0, support was added in the device hardware (via the Hot
> Reset Disable Bit) to allow resetting only the PCIe interface and its
> associated logic, but preserving the UART configuration during a hot
> reset. This patch enables the hot reset disable feature during suspend/
> resume for C0 and later revisions of the device.
> 
> Signed-off-by: Rengarajan S <rengarajan.s@microchip.com>
> ---
>   drivers/tty/serial/8250/8250_pci1xxxx.c | 18 ++++++++++++++++--
>   1 file changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/tty/serial/8250/8250_pci1xxxx.c b/drivers/tty/serial/8250/8250_pci1xxxx.c
> index e9c51d4e447d..ec573327590f 100644
> --- a/drivers/tty/serial/8250/8250_pci1xxxx.c
> +++ b/drivers/tty/serial/8250/8250_pci1xxxx.c
> @@ -115,6 +115,7 @@
>   
>   #define UART_RESET_REG				0x94
>   #define UART_RESET_D3_RESET_DISABLE		BIT(16)
> +#define UART_RESET_HOT_RESET_DISABLE            BIT(17)
>   
>   #define UART_BURST_STATUS_REG			0x9C
>   #define UART_TX_BURST_FIFO			0xA0
> @@ -620,7 +621,13 @@ static int pci1xxxx_suspend(struct device *dev)
>   	}
>   
>   	data = readl(p + UART_RESET_REG);
> -	writel(data | UART_RESET_D3_RESET_DISABLE, p + UART_RESET_REG);
> +
> +	if (priv->dev_rev >= 0xC0)
> +		writel(data | (UART_RESET_D3_RESET_DISABLE |
> +		       UART_RESET_HOT_RESET_DISABLE), p + UART_RESET_REG);
> +	else
> +		writel(data | UART_RESET_D3_RESET_DISABLE,
> +		       p + UART_RESET_REG);

Instead of this overly long lines, could you just:
   data |= UART_RESET_HOT_RESET_DISABLE;
and keep the writel() as is?

thanks,
-- 
js
suse labs

Re: [PATCH v1 tty-next] 8250: microchip: pci1xxxx: Add PCIe Hot reset disable support for Rev C0 and later devices

Posted by Rengarajan.S@microchip.com 9 months, 2 weeks ago

Hi Jiri Slaby,

Thanks for reviewing the patch.

On Wed, 2025-04-23 at 07:11 +0200, Jiri Slaby wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you
> know the content is safe
> 
> On 23. 04. 25, 5:38, Rengarajan S wrote:
> > Systems that issue PCIe hot reset requests during a suspend/resume
> > cycle cause PCI1XXXX device revisions prior to C0 to get its UART
> > configuration registers reset to hardware default values. This
> > results
> > in device inaccessibility and data transfer failures. Starting with
> > Revision C0, support was added in the device hardware (via the Hot
> > Reset Disable Bit) to allow resetting only the PCIe interface and
> > its
> > associated logic, but preserving the UART configuration during a
> > hot
> > reset. This patch enables the hot reset disable feature during
> > suspend/
> > resume for C0 and later revisions of the device.
> > 
> > Signed-off-by: Rengarajan S <rengarajan.s@microchip.com>
> > ---
> >   drivers/tty/serial/8250/8250_pci1xxxx.c | 18 ++++++++++++++++--
> >   1 file changed, 16 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/tty/serial/8250/8250_pci1xxxx.c
> > b/drivers/tty/serial/8250/8250_pci1xxxx.c
> > index e9c51d4e447d..ec573327590f 100644
> > --- a/drivers/tty/serial/8250/8250_pci1xxxx.c
> > +++ b/drivers/tty/serial/8250/8250_pci1xxxx.c
> > @@ -115,6 +115,7 @@
> > 
> >   #define UART_RESET_REG                              0x94
> >   #define UART_RESET_D3_RESET_DISABLE         BIT(16)
> > +#define UART_RESET_HOT_RESET_DISABLE            BIT(17)
> > 
> >   #define UART_BURST_STATUS_REG                       0x9C
> >   #define UART_TX_BURST_FIFO                  0xA0
> > @@ -620,7 +621,13 @@ static int pci1xxxx_suspend(struct device
> > *dev)
> >       }
> > 
> >       data = readl(p + UART_RESET_REG);
> > -     writel(data | UART_RESET_D3_RESET_DISABLE, p +
> > UART_RESET_REG);
> > +
> > +     if (priv->dev_rev >= 0xC0)
> > +             writel(data | (UART_RESET_D3_RESET_DISABLE |
> > +                    UART_RESET_HOT_RESET_DISABLE), p +
> > UART_RESET_REG);
> > +     else
> > +             writel(data | UART_RESET_D3_RESET_DISABLE,
> > +                    p + UART_RESET_REG);
> 
> Instead of this overly long lines, could you just:
>    data |= UART_RESET_HOT_RESET_DISABLE;
> and keep the writel() as is?

Sure will update the code in the next revision.

> 
> thanks,
> --
> js
> suse labs