Re: [Qemu-devel] [PATCH 5/6] hw/arm/sysbus-fdt: helpers for clock node generation

[Eric Auger <eric.auger@linaro.org>]

On 12/18/2015 03:54 PM, Peter Maydell wrote:
> On 17 December 2015 at 12:29, Eric Auger <eric.auger@linaro.org> wrote:
>> Some passthrough'ed devices depend on clock nodes. Those need to be
>> generated in the guest device tree. This patch introduces some helpers
>> to build a clock node from information retrieved in the host device tree.
>>
>> - inherit_properties copies properties from a host device tree node to
>>   a guest device tree node
>> - fdt_build_clock_node builds a guest clock node and checks the host
>>   fellow clock is a fixed one.
>>
>> fdt_build_clock_node will become static as soon as it gets used. A
>> dummy pre-declaration is needed for compilation of this patch.
>>
>> Signed-off-by: Eric Auger <eric.auger@linaro.org>
>>
>> ---
>>
>> RFC -> v1:
>> - use the new proto of qemu_fdt_getprop
>> - remove newline in error_report
>> - fix some style issues
>> ---
>>  hw/arm/sysbus-fdt.c | 111 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>>  1 file changed, 111 insertions(+)
>>
>> diff --git a/hw/arm/sysbus-fdt.c b/hw/arm/sysbus-fdt.c
>> index 9d28797..c2d813b 100644
>> --- a/hw/arm/sysbus-fdt.c
>> +++ b/hw/arm/sysbus-fdt.c
>> @@ -21,6 +21,7 @@
>>   *
>>   */
>>
>> +#include <libfdt.h>
>>  #include "hw/arm/sysbus-fdt.h"
>>  #include "qemu/error-report.h"
>>  #include "sysemu/device_tree.h"
>> @@ -56,6 +57,116 @@ typedef struct NodeCreationPair {
>>      int (*add_fdt_node_fn)(SysBusDevice *sbdev, void *opaque);
>>  } NodeCreationPair;
>>
>> +/* helpers */
>> +
>> +struct HostProperty {
>> +    const char *name;
>> +    bool optional;
>> +};
>> +
>> +typedef struct HostProperty HostProperty;
> 
> You can combine the typedef and the struct declaration if you like.

ok
> 
>> +
>> +/**
>> + * inherit_properties
>> + *
>> + * copies properties listed in an array from host device tree to
>> + * guest device tree. If a non optional property is not found, the
>> + * function self-asserts. An optional property is ignored if not found
>> + * in the host device tree.
>> + * @props: array of HostProperty to copy
>> + * @nb_props: number of properties in the array
>> + * @host_dt: host device tree blob
>> + * @guest_dt: guest device tree blob
>> + * @node_path: host dt node path where the property is supposed to be
>> +              found
>> + * @nodename: guest node name the properties should be added to
>> + */
>> +static void inherit_properties(HostProperty *props, int nb_props,
>> +                               void *host_fdt, void *guest_fdt,
>> +                               char *node_path, char *nodename)
>> +{
>> +    int i, prop_len;
>> +    const void *r;
>> +
>> +    for (i = 0; i < nb_props; i++) {
>> +        r = qemu_fdt_getprop(host_fdt, node_path,
>> +                             props[i].name,
>> +                             &prop_len,
>> +                             props[i].optional ? NULL : &error_fatal);
> 
> We'll get an error here if the host device tree doesn't match
> up correctly, right? Is the error message going to be sufficiently
> informative to the end user about what's gone wrong? (What does
> it end up looking like?)

hum you're right, in case of a mandated property there is auto-assert
with a good error message.
In case of an optional property, there is currently no message output to
the end-user and the host property is ignored/not propagated to the
guest, with potential functional consequences.  I intend to use an error
object instead and print the error message in case the error is !=
FDT_ERR_NOTFOUND.
> 
>> +        if (r) {
>> +            qemu_fdt_setprop(guest_fdt, nodename,
>> +                             props[i].name, r, prop_len);
>> +        }
>> +    }
>> +}
>> +
>> +/* clock properties whose values are copied/pasted from host */
>> +static HostProperty clock_inherited_properties[] = {
>> +    {"compatible", 0},
>> +    {"#clock-cells", 0},
>> +    {"clock-frequency", 1},
>> +    {"clock-output-names", 1},
>> +};
>> +
>> +/**
>> + * fdt_build_clock_node
>> + *
>> + * Build a guest clock node, used as a dependency from a passthrough'ed
>> + * device. Most information are retrieved from the host clock node.
>> + * Also check the host clock is a fixed one.
>> + *
>> + * @host_fdt: host device tree blob from which info are retrieved
>> + * @guest_fdt: guest device tree blob where the clock node is added
>> + * @host_phandle: phandle of the clock in host device tree
>> + * @guest_phandle: phandle to assign to the guest node
>> + */
>> +int fdt_build_clock_node(void *host_fdt, void *guest_fdt,
>> +                         uint32_t host_phandle,
>> +                         uint32_t guest_phandle);
>> +int fdt_build_clock_node(void *host_fdt, void *guest_fdt,
>> +                         uint32_t host_phandle,
>> +                         uint32_t guest_phandle)
>> +{
>> +    char node_path[256];
> 
> Please don't use hardcoded fixed buffer lengths (see previous patch
> review comments).
OK
> 
>> +    char *nodename;
>> +    const void *r;
>> +    int ret, prop_len;
>> +
>> +    ret = fdt_node_offset_by_phandle(host_fdt, host_phandle);
>> +    if (ret <= 0) {
>> +        error_report("not able to locate clock handle %d in host device tree",
>> +                     host_phandle);
>> +        goto out;
>> +    }
> 
> If we're going to return to the caller in the error case rather than just
> exiting here, I think we should return the error to the caller via an
> Error** rather than calling error_report() directly ourselves.
agreed

Thanks!

Eric
> 
>> +    ret = fdt_get_path(host_fdt, ret, node_path, 256);
>> +    if (ret < 0) {
>> +        error_report("not able to retrieve node path for clock handle %d",
>> +                     host_phandle);
>> +        goto out;
>> +    }
>> +
>> +    r = qemu_fdt_getprop(host_fdt, node_path, "compatible", &prop_len,
>> +                         &error_fatal);
>> +    if (strcmp(r, "fixed-clock")) {
>> +        error_report("clock handle %d is not a fixed clock", host_phandle);
>> +        ret = -1;
>> +        goto out;
>> +    }
>> +
>> +    nodename = strrchr(node_path, '/');
>> +    qemu_fdt_add_subnode(guest_fdt, nodename);
>> +
>> +    inherit_properties(clock_inherited_properties,
>> +                       ARRAY_SIZE(clock_inherited_properties),
>> +                       host_fdt, guest_fdt,
>> +                       node_path, nodename);
>> +
>> +    qemu_fdt_setprop_cell(guest_fdt, nodename, "phandle", guest_phandle);
>> +
>> +out:
>> +    return ret;
>> +}
>> +
>>  /* Device Specific Code */
> 
> thanks
> -- PMM
>