Re: [Qemu-devel] [PATCH v4 3/8] fw_cfg: introduce the "data_memwidth" property

[Laszlo Ersek <lersek@redhat.com>]

On 12/16/14 13:06, Alexander Graf wrote:
> 
> 
> On 12.12.14 16:58, Laszlo Ersek wrote:
>> The "data_memwidth" property is capable of changing the maximum valid
>> access size to the MMIO data register, and (corresponding to the previous
>> patch) resizes the memory region similarly, at device realization time.
>>
>> (Because "data_iomem" is configured and installed dynamically now, we must
>> delay those steps to the realize callback.)
>>
>> The default value of "data_memwidth" is set so that we don't yet diverge
>> from "fw_cfg_data_mem_ops".
>>
>> Most of the fw_cfg users will stick with the default, and for them we
>> should continue using the statically allocated "fw_cfg_data_mem_ops". This
>> is beneficial for debugging because gdb can resolve pointers referencing
>> static objects to the names of those objects.
>>
>> Signed-off-by: Laszlo Ersek <lersek@redhat.com>
>> ---
>>
>> Notes:
>>     v4:
>>     - reject I/O port combining if data register is wider than 1 byte
>>       [Peter]
>>     
>>     v3:
>>     - new in v3 [Drew Jones]
>>
>>  hw/nvram/fw_cfg.c | 24 ++++++++++++++++++------
>>  1 file changed, 18 insertions(+), 6 deletions(-)
>>
>> diff --git a/hw/nvram/fw_cfg.c b/hw/nvram/fw_cfg.c
>> index eb0ad83..0947136 100644
>> --- a/hw/nvram/fw_cfg.c
>> +++ b/hw/nvram/fw_cfg.c
>> @@ -50,8 +50,9 @@ struct FWCfgState {
>>      /*< public >*/
>>  
>>      MemoryRegion ctl_iomem, data_iomem, comb_iomem;
>>      uint32_t ctl_iobase, data_iobase;
>> +    uint32_t data_memwidth;
>>      FWCfgEntry entries[2][FW_CFG_MAX_ENTRY];
>>      FWCfgFiles *files;
>>      uint16_t cur_entry;
>>      uint32_t cur_offset;
>> @@ -569,8 +570,10 @@ FWCfgState *fw_cfg_init(uint32_t ctl_port, uint32_t data_port,
>>  
>>      dev = qdev_create(NULL, TYPE_FW_CFG);
>>      qdev_prop_set_uint32(dev, "ctl_iobase", ctl_port);
>>      qdev_prop_set_uint32(dev, "data_iobase", data_port);
>> +    qdev_prop_set_uint32(dev, "data_memwidth",
>> +                         fw_cfg_data_mem_ops.valid.max_access_size);
>>      d = SYS_BUS_DEVICE(dev);
>>  
>>      s = FW_CFG(dev);
>>  
>> @@ -607,12 +610,8 @@ static void fw_cfg_initfn(Object *obj)
>>  
>>      memory_region_init_io(&s->ctl_iomem, OBJECT(s), &fw_cfg_ctl_mem_ops, s,
>>                            "fwcfg.ctl", FW_CFG_SIZE);
>>      sysbus_init_mmio(sbd, &s->ctl_iomem);
>> -    memory_region_init_io(&s->data_iomem, OBJECT(s), &fw_cfg_data_mem_ops, s,
>> -                          "fwcfg.data",
>> -                          fw_cfg_data_mem_ops.valid.max_access_size);
>> -    sysbus_init_mmio(sbd, &s->data_iomem);
>>      /* In case ctl and data overlap: */
>>      memory_region_init_io(&s->comb_iomem, OBJECT(s), &fw_cfg_comb_mem_ops, s,
>>                            "fwcfg", FW_CFG_SIZE);
>>  }
>> @@ -620,19 +619,31 @@ static void fw_cfg_initfn(Object *obj)
>>  static void fw_cfg_realize(DeviceState *dev, Error **errp)
>>  {
>>      FWCfgState *s = FW_CFG(dev);
>>      SysBusDevice *sbd = SYS_BUS_DEVICE(dev);
>> +    const MemoryRegionOps *data_mem_ops = &fw_cfg_data_mem_ops;
>>      uint32_t ctl_io_last;
>>      uint32_t data_io_end;
>>  
>> +    if (s->data_memwidth > data_mem_ops->valid.max_access_size) {
>> +        MemoryRegionOps *ops;
>> +
>> +        ops = g_memdup(data_mem_ops, sizeof(*data_mem_ops));
> 
> Hrm, this memory will leak if the device gets destroyed after realize,
> right?

How do you destroy the fw_cfg device after it is successfully realized?
I wouldn't introduce such a blatant leak out of oversight.

> I see 2 options around this:
> 
>   1) Free it on destruction

Does that mean an unrealize callback?

>   2) Add the RegionOps as field into FWCfgState. Then it gets allocated
> and free'd automatically
> 
> Option 2 is easier (and more failure proof) but will waste a few bytes
> of ram for data_memwidth=1 users. I don't think we need to bother about
> the few bytes and rather go with safety :).

I wanted to keep the static ops object for the common user, because it
is very convenient when debugging in gdb -- the address is automatically
resolved to the name of the static object. I guess I can do (1) (if that
means an unrealize callback).

Thanks
Laszlo