[v6,1/2] xen/riscv: introduce early_printk basic stuff

Commit Message

Oleksii Kurochko Jan. 27, 2023, 11:15 a.m. UTC

Because printk() relies on a serial driver (like the ns16550 driver)
and drivers require working virtual memory (ioremap()) there is not
print functionality early in Xen boot.

The patch introduces the basic stuff of early_printk functionality
which will be enough to print 'hello from C environment".

Originally early_printk.{c,h} was introduced by Bobby Eshleman
(https://github.com/glg-rv/xen/commit/a3c9916bbdff7ad6030055bbee7e53d1aab71384)
but some functionality was changed:
early_printk() function was changed in comparison with the original as
common isn't being built now so there is no vscnprintf.

This commit adds early printk implementation built on the putc SBI call.

As sbi_console_putchar() is already being planned for deprecation
it is used temporarily now and will be removed or reworked after
real uart will be ready.

Signed-off-by: Bobby Eshleman <[e-mail]>
Signed-off-by: Oleksii Kurochko <[e-mail]>
Reviewed-by: Bobby Eshleman <[e-mail]>
---
Changes in V6:
    - Remove __riscv_cmodel_medany check from early_printk.c
---
Changes in V5:
    - Code style fixes
    - Change an error message of #error in case of __riscv_cmodel_medany
      isn't defined
---
Changes in V4:
    - Remove "depends on RISCV*" from Kconfig.debug as it is located in
      arch specific folder so by default RISCV configs should be ebabled.
    - Add "ifdef __riscv_cmodel_medany" to be sure that PC-relative addressing
      is used as early_*() functions can be called from head.S with MMU-off and
      before relocation (if it would be needed at all for RISC-V)
    - fix code style
---
Changes in V3:
    - reorder headers in alphabetical order
    - merge changes related to start_xen() function from "[PATCH v2 7/8]
      xen/riscv: print hello message from C env" to this patch
    - remove unneeded parentheses in definition of STACK_SIZE
---
Changes in V2:
    - introduce STACK_SIZE define.
    - use consistent padding between instruction mnemonic and operand(s)
---
 xen/arch/riscv/Kconfig.debug              |  5 ++++
 xen/arch/riscv/Makefile                   |  1 +
 xen/arch/riscv/early_printk.c             | 33 +++++++++++++++++++++++
 xen/arch/riscv/include/asm/early_printk.h | 12 +++++++++
 xen/arch/riscv/setup.c                    |  4 +++
 5 files changed, 55 insertions(+)
 create mode 100644 xen/arch/riscv/early_printk.c
 create mode 100644 xen/arch/riscv/include/asm/early_printk.h

Comments

Julien Grall Jan. 27, 2023, 11:26 a.m. UTC | #1

Hi,

On 27/01/2023 11:15, Oleksii Kurochko wrote:
> Because printk() relies on a serial driver (like the ns16550 driver)
> and drivers require working virtual memory (ioremap()) there is not
> print functionality early in Xen boot.
> 
> The patch introduces the basic stuff of early_printk functionality
> which will be enough to print 'hello from C environment".
> 
> Originally early_printk.{c,h} was introduced by Bobby Eshleman
> (https://github.com/glg-rv/xen/commit/a3c9916bbdff7ad6030055bbee7e53d1aab71384)
> but some functionality was changed:
> early_printk() function was changed in comparison with the original as
> common isn't being built now so there is no vscnprintf.
> 
> This commit adds early printk implementation built on the putc SBI call.
> 
> As sbi_console_putchar() is already being planned for deprecation
> it is used temporarily now and will be removed or reworked after
> real uart will be ready.
> 
> Signed-off-by: Bobby Eshleman <[e-mail]>
> Signed-off-by: Oleksii Kurochko <[e-mail]>
> Reviewed-by: Bobby Eshleman <[e-mail]>
> ---
> Changes in V6:
>      - Remove __riscv_cmodel_medany check from early_printk.c

Why? I know Andrew believed this is wrong, but I replied back with my 
understanding and saw no discussion afterwards explaining why I am 
incorrect.

I am not a maintainer of the code here, but I don't particularly 
appreciate comments to be ignored. If there was any discussion on IRC, 
then please summarize them here.

Cheers,

Oleksii Kurochko Jan. 27, 2023, 11:49 a.m. UTC | #2

On Fri, 2023-01-27 at 11:26 +0000, Julien Grall wrote:
> Hi,
> 
> On 27/01/2023 11:15, Oleksii Kurochko wrote:
> > Because printk() relies on a serial driver (like the ns16550
> > driver)
> > and drivers require working virtual memory (ioremap()) there is not
> > print functionality early in Xen boot.
> > 
> > The patch introduces the basic stuff of early_printk functionality
> > which will be enough to print 'hello from C environment".
> > 
> > Originally early_printk.{c,h} was introduced by Bobby Eshleman
> > (
> > https://github.com/glg-rv/xen/commit/a3c9916bbdff7ad6030055bbee7e53d
> > 1aab71384)
> > but some functionality was changed:
> > early_printk() function was changed in comparison with the original
> > as
> > common isn't being built now so there is no vscnprintf.
> > 
> > This commit adds early printk implementation built on the putc SBI
> > call.
> > 
> > As sbi_console_putchar() is already being planned for deprecation
> > it is used temporarily now and will be removed or reworked after
> > real uart will be ready.
> > 
> > Signed-off-by: Bobby Eshleman <[e-mail]>
> > Signed-off-by: Oleksii Kurochko <[e-mail]>
> > Reviewed-by: Bobby Eshleman <[e-mail]>
> > ---
> > Changes in V6:
> >      - Remove __riscv_cmodel_medany check from early_printk.c
> 
> Why? I know Andrew believed this is wrong, but I replied back with my
> understanding and saw no discussion afterwards explaining why I am 
> incorrect.
> 
> I am not a maintainer of the code here, but I don't particularly 
> appreciate comments to be ignored. If there was any discussion on
> IRC, 
> then please summarize them here.
Sorry, I have to mentioned that in the description of patch series.

There is no any specific reason to remove and only one reason I decided
to remove the check was that the check wasn't present in original
Alistair/Bobby patches and based on my experiments with that patches 
all worked fine. ( at least with some additional patches from my side I
was able to run Dom0 with console )

I pushed a new version (v7) of the patch series ( as I missed to change
dependency for CI job ) so probably we have to open a discussion again
as Andrew don't answer for a long time.
> 
> Cheers,
> 
~ Oleksii

Julien Grall Jan. 27, 2023, 12:22 p.m. UTC | #3

Hi Oleksii,

On 27/01/2023 11:49, Oleksii wrote:
> On Fri, 2023-01-27 at 11:26 +0000, Julien Grall wrote:
>> Hi,
>>
>> On 27/01/2023 11:15, Oleksii Kurochko wrote:
>>> Because printk() relies on a serial driver (like the ns16550
>>> driver)
>>> and drivers require working virtual memory (ioremap()) there is not
>>> print functionality early in Xen boot.
>>>
>>> The patch introduces the basic stuff of early_printk functionality
>>> which will be enough to print 'hello from C environment".
>>>
>>> Originally early_printk.{c,h} was introduced by Bobby Eshleman
>>> (
>>> https://github.com/glg-rv/xen/commit/a3c9916bbdff7ad6030055bbee7e53d
>>> 1aab71384)
>>> but some functionality was changed:
>>> early_printk() function was changed in comparison with the original
>>> as
>>> common isn't being built now so there is no vscnprintf.
>>>
>>> This commit adds early printk implementation built on the putc SBI
>>> call.
>>>
>>> As sbi_console_putchar() is already being planned for deprecation
>>> it is used temporarily now and will be removed or reworked after
>>> real uart will be ready.
>>>
>>> Signed-off-by: Bobby Eshleman <[e-mail]>
>>> Signed-off-by: Oleksii Kurochko <[e-mail]>
>>> Reviewed-by: Bobby Eshleman <[e-mail]>
>>> ---
>>> Changes in V6:
>>>       - Remove __riscv_cmodel_medany check from early_printk.c
>>
>> Why? I know Andrew believed this is wrong, but I replied back with my
>> understanding and saw no discussion afterwards explaining why I am
>> incorrect.
>>
>> I am not a maintainer of the code here, but I don't particularly
>> appreciate comments to be ignored. If there was any discussion on
>> IRC,
>> then please summarize them here.
> Sorry, I have to mentioned that in the description of patch series.

I think this should be part of the section --- in this patch as this 
makes easier to know what changes have been done.

> 
> There is no any specific reason to remove and only one reason I decided
> to remove the check was that the check wasn't present in original
> Alistair/Bobby patches and based on my experiments with that patches
> all worked fine. ( at least with some additional patches from my side I
> was able to run Dom0 with console )

The lines you removed only confirm that the file was built with the 
given model and if it is incorrect then the compilation will fail. There 
are no change in behavior expected past the compilation.

So I am not quite too sure what sort of experiment you did. Did you try 
to change the model used to build Xen?

Now if you (or anyone else) can tell me that there will be no issues if 
the model is changed. Then yes, I will agree that the check is unnecessary.

The alternative is you say that you are happy to accept the risk if the 
model is changed. If I were the maintainer, that would not be something 
I would agree with because "wrong" unwritten assumptions are a pain to 
debug. So I much prefer a "wrong" written assumptions that would tip me 
that the author thought the code would not work otherwise.

This is quite easy to remove the check after the fact if it is not correct.

I am not the maintainer of the code, so if this is what they want then 
so be it. But it needs to be explicitely stated. So far, the reviewed-by 
from Bobby was with the check, so it would imply that he was happy with 
it...

Cheers,

Patch

diff --git a/xen/arch/riscv/Kconfig.debug b/xen/arch/riscv/Kconfig.debug
index e69de29bb2..608c9ff832 100644
--- a/xen/arch/riscv/Kconfig.debug
+++ b/xen/arch/riscv/Kconfig.debug
@@ -0,0 +1,5 @@ 
+config EARLY_PRINTK
+    bool "Enable early printk"
+    default DEBUG
+    help
+      Enables early printk debug messages
diff --git a/xen/arch/riscv/Makefile b/xen/arch/riscv/Makefile
index fd916e1004..1a4f1a6015 100644
--- a/xen/arch/riscv/Makefile
+++ b/xen/arch/riscv/Makefile
@@ -1,3 +1,4 @@ 
+obj-$(CONFIG_EARLY_PRINTK) += early_printk.o
 obj-$(CONFIG_RISCV_64) += riscv64/
 obj-y += sbi.o
 obj-y += setup.o
diff --git a/xen/arch/riscv/early_printk.c b/xen/arch/riscv/early_printk.c
new file mode 100644
index 0000000000..b66a11f1bc
--- /dev/null
+++ b/xen/arch/riscv/early_printk.c
@@ -0,0 +1,33 @@ 
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * RISC-V early printk using SBI
+ *
+ * Copyright (C) 2021 Bobby Eshleman <[e-mail]>
+ */
+#include <asm/early_printk.h>
+#include <asm/sbi.h>
+
+/*
+ * TODO:
+ *   sbi_console_putchar is already planned for deprecation
+ *   so it should be reworked to use UART directly.
+*/
+void early_puts(const char *s, size_t nr)
+{
+    while ( nr-- > 0 )
+    {
+        if ( *s == '\n' )
+            sbi_console_putchar('\r');
+        sbi_console_putchar(*s);
+        s++;
+    }
+}
+
+void early_printk(const char *str)
+{
+    while ( *str )
+    {
+        early_puts(str, 1);
+        str++;
+    }
+}
diff --git a/xen/arch/riscv/include/asm/early_printk.h b/xen/arch/riscv/include/asm/early_printk.h
new file mode 100644
index 0000000000..05106e160d
--- /dev/null
+++ b/xen/arch/riscv/include/asm/early_printk.h
@@ -0,0 +1,12 @@ 
+#ifndef __EARLY_PRINTK_H__
+#define __EARLY_PRINTK_H__
+
+#include <xen/early_printk.h>
+
+#ifdef CONFIG_EARLY_PRINTK
+void early_printk(const char *str);
+#else
+static inline void early_printk(const char *s) {};
+#endif
+
+#endif /* __EARLY_PRINTK_H__ */
diff --git a/xen/arch/riscv/setup.c b/xen/arch/riscv/setup.c
index 13e24e2fe1..d09ffe1454 100644
--- a/xen/arch/riscv/setup.c
+++ b/xen/arch/riscv/setup.c
@@ -1,12 +1,16 @@ 
 #include <xen/compile.h>
 #include <xen/init.h>
 
+#include <asm/early_printk.h>
+
 /* Xen stack for bringing up the first CPU. */
 unsigned char __initdata cpu0_boot_stack[STACK_SIZE]
     __aligned(STACK_SIZE);
 
 void __init noreturn start_xen(void)
 {
+    early_printk("Hello from C env\n");
+
     for ( ;; )
         asm volatile ("wfi");