Re: [Xen-devel] [PATCH RFC 12/15] xen/arm: generate vpl011 node on device tree for domU

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Fri, 15 Jun 2018, Julien Grall wrote:
> Hi Stefano,
> 
> On 06/13/2018 11:15 PM, Stefano Stabellini wrote:
> > Introduce vpl011 support to guests started from Xen: it provides a
> > simple way to print output from a guest, as most guests come with a
> > pl011 driver. It is also able to provide a working console with
> > interrupt support.
> > 
> > Signed-off-by: Stefano Stabellini <stefanos@xxxxxxxxxx>
> > ---
> >   xen/arch/arm/domain_build.c | 70
> > +++++++++++++++++++++++++++++++++++++++++++++
> >   1 file changed, 70 insertions(+)
> > 
> > diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
> > index b4f560f..ff65057 100644
> > --- a/xen/arch/arm/domain_build.c
> > +++ b/xen/arch/arm/domain_build.c
> > @@ -1470,6 +1470,70 @@ static int make_timer_domU_node(const struct domain
> > *d, void *fdt)
> >       return res;
> >   }
> >   +static void set_interrupt(gic_interrupt_t *interrupt, unsigned int irq,
> 
> The definition of interrupt looks suspicious. gic_interrupt_t is defined as
> be32[3]. Here you pass a pointer, so interrupt type would be __be32 **, that
> you crudely cast to __be32* below.
> 
> Most likely you don't want to pass a pointer here and just use the type
> gic_interrupt_t. Because it is an array, then there will be no issue.

Right, I'll fix


> > +                          unsigned int cpumask, unsigned int level)
> > +{
> > +    __be32 *cells = (__be32 *) interrupt;
> 
> Explicit cast are always a bad idea. If you need one, then mostly likely you
> did something wrong :). In that case interrupt type is __be32** and you cast
> to __be32*. If you change the type as suggested above, then the cast will not
> be necessary here.

Yeah


> > +    int is_ppi = (irq < 32);
> > +
> > +    irq -= (is_ppi) ? 16: 32; /* PPIs start at 16, SPIs at 32 */
> > +
> > +    /* See linux Documentation/devictree/bindings/arm/gic.txt */
> > +    dt_set_cell(&cells, 1, is_ppi); /* is a PPI? */
> > +    dt_set_cell(&cells, 1, irq);
> > +    dt_set_cell(&cells, 1, (cpumask << 8) | level);
> > +}
> 
> We already have a function to generate PPI interrupt (set_interrupt_ppi).
> Would it be possible to extend it to support interrupt?
> 
> Most likely, you will want to use set_interrupt(...) everywhere and just drop
> set_interrupt_ppi.

Good idea, I'll remove set_interrupt_ppi

> > +
> > +#ifdef CONFIG_SBSA_VUART_CONSOLE
> > +static int make_vpl011_uart_node(const struct domain *d, void *fdt,
> > +                                 int addrcells, int sizecells)
> > +{
> > +    int res;
> > +    gic_interrupt_t intr;
> > +    int reg_size = addrcells + sizecells;
> > +    int nr_cells = reg_size;
> > +    __be32 reg[nr_cells];
> > +    __be32 *cells;
> > +
> > +    res = fdt_begin_node(fdt, "sbsa-pl011");
> > +    if (res)
> 
> Coding style:
> 
> if ( ... )
> 
> > +        return res;
> > +
> > +    res = fdt_property_string(fdt, "compatible", "arm,sbsa-uart");
> 
> To make clear, you are exposing a SBSA compatible UART and not a PL011. SBSA
> UART is a subset of PL011 r1p5. A full PL011 implementation in Xen would just
> be too difficult, so your guest may require some changes in their driver.
> 
> I think this is a small price to pay, but I wanted to make sure you don't
> expect the guest to drive the UART the same way a PL011.

I'll add a note to the commit message


> > +    if (res)
> 
> Coding style
> 
> > +        return res;
> > +
> > +    cells = &reg[0];
> > +    dt_child_set_range(&cells, addrcells, sizecells, GUEST_PL011_BASE,
> > +            GUEST_PL011_SIZE);
> 
> The indentation looks wrong here.
> 
> > +    if (res)
> 
> Coding style
> 
> > +        return res;
> > +    res = fdt_property(fdt, "reg", reg, sizeof(reg));
> > +    if (res)
> 
> Coding style
> 
> > +        return res;
> > +
> > +    set_interrupt(&intr, GUEST_VPL011_SPI, 0xf, DT_IRQ_TYPE_LEVEL_HIGH);
> > +
> > +    res = fdt_property(fdt, "interrupts", intr, sizeof (intr));
> > +    if (res)
> 
> Coding style
> 
> > +        return res;
> > +
> > +    res = fdt_property_cell(fdt, "interrupt-parent",
> > +                            PHANDLE_GIC);
> > +    if (res)
> 
> Coding style
> 
> > +        return res;
> > +
> > +    /* Use a default baud rate of 115200. */
> > +    fdt_property_u32(fdt, "current-speed", 115200);
> > +
> > +    res = fdt_end_node(fdt);
> > +    if (res)
> 
> Coding style

Fixed them all


> > +        return res;
> > +
> > +    return 0;
> > +}
> > +#endif
> > +
> >   #define DOMU_DTB_SIZE 4096
> >   static int prepare_dtb_domU(struct domain *d, struct kernel_info *kinfo)
> >   {
> > @@ -1531,6 +1595,12 @@ static int prepare_dtb_domU(struct domain *d, struct
> > kernel_info *kinfo)
> >       if ( ret )
> >           goto err;
> >   +#ifdef CONFIG_SBSA_VUART_CONSOLE.
> > +    ret = make_vpl011_uart_node(d, kinfo->fdt, addrcells, sizecells);
> 
> I would prefer if don't expose the pl011 by default to a guest and provide a
> way to enable it for a given guest

I'll add a vpl011 option


> > +    if ( ret )
> > +        goto err;
> > +#endif
> > +
> >       ret = fdt_end_node(kinfo->fdt);
> >       if ( ret < 0 )
> >           goto err;
> > 
> 
> Cheers,
> 
> -- 
> Julien Grall
> 

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