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Re: [Xen-devel] [PATCH v2 18/21] xen/arm: Allow vpl011 to be used by DomU

Hi Stefano,

On 27/07/18 01:10, Stefano Stabellini wrote:
On Tue, 24 Jul 2018, Julien Grall wrote:
On 07/07/18 00:12, Stefano Stabellini wrote:
+    VPL011_UNLOCK(d, flags);
+static void vpl011_write_data_noring(struct domain *d, uint8_t data)
+    unsigned long flags;
+    struct vpl011 *vpl011 = &d->arch.vpl011;
+    VPL011_LOCK(d, flags);
+    printk("%c", data);
+    if (data == '\n')
+        printk("DOM%u: ", d->domain_id);

You want to buffer the characters here and only print on newline or when the
buffer is full. Otherwise characters will get mangled with the Xen console
output or other domains output.

I did the implementation, but then when I type characters at the domain
prompt, I don't see them anymore one by one. Only after I press
"enter". That makes the domain console not very usable. Should we keep
it as?

I haven't thought about that case. However, if you don't implement the buffer solution, you will get all the domain consoles mangled during boot. This is not really nice for debugging. A potential solution is to buffer for all the domains but the one that is reading characters.

+    vpl011->uartris |= TXI;
+    vpl011->uartfr &= ~TXFE;
+    vpl011_update_interrupt_status(d);
+    VPL011_UNLOCK(d, flags);
+static uint8_t vpl011_read_data_inring(struct domain *d)

I think you can avoid the duplication here by using a macro.

I prefer to avoid MACROS for things like this. I would rather reuse the
existing function for both cases like in v1. Would you be OK to go back
to that?

I would rather keep the duplication over going back to v1.

I may have another way to keep the code common, but let's look at that in a latter patch. For now, I will deal with the duplication.


Julien Grall

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