Re: [PATCH v4 08/23] ata: libahci_platform: Sanity check the DT child nodes number

Damien Le Moal
2022-06-16T00:25:58Z

On 2022/06/16 5:53, Serge Semin wrote:
> On Tue, Jun 14, 2022 at 05:23:33PM +0900, Damien Le Moal wrote:
>> On 6/10/22 17:17, Serge Semin wrote:
>>> Having greater than AHCI_MAX_PORTS (32) ports detected isn't that critical
>>> from the further AHCI-platform initialization point of view since
>>> exceeding the ports upper limit will cause allocating more resources than
>>> will be used afterwards. But detecting too many child DT-nodes doesn't
>>> seem right since it's very unlikely to have it on an ordinary platform. In
>>> accordance with the AHCI specification there can't be more than 32 ports
>>> implemented at least due to having the CAP.NP field of 5 bits wide and the
>>> PI register of dword size. Thus if such situation is found the DTB must
>>> have been corrupted and the data read from it shouldn't be reliable. Let's
>>> consider that as an erroneous situation and halt further resources
>>> allocation.
>>>
>>> Note it's logically more correct to have the nports set only after the
>>> initialization value is checked for being sane. So while at it let's make
>>> sure nports is assigned with a correct value.
>>>
>>> Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
>>> Reviewed-by: Hannes Reinecke <hare@suse.de>
>>>
>>> ---
>>>
>>> Changelog v2:
>>> - Drop the else word from the child_nodes value checking if-else-if
>>> statement (@Damien) and convert the after-else part into the ternary
>>> operator-based statement.
>>>
>>> Changelog v4:
>>> - Fix some logical mistakes in the patch log. (@Sergei Shtylyov)
>>> ---
>>> drivers/ata/libahci_platform.c | 13 ++++++++++---
>>> 1 file changed, 10 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/ata/libahci_platform.c b/drivers/ata/libahci_platform.c
>>> index 814804582d1d..8aed7b29c7ab 100644
>>> --- a/drivers/ata/libahci_platform.c
>>> +++ b/drivers/ata/libahci_platform.c
>>> @@ -451,15 +451,22 @@ struct ahci_host_priv *ahci_platform_get_resources(struct platform_device *pdev,
>>> }
>>> }
>>>
>>> - hpriv->nports = child_nodes = of_get_child_count(dev->of_node);
>>> + /*
>>> + * Too many sub-nodes most likely means having something wrong with
>>> + * the firmware.
>>> + */
>>> + child_nodes = of_get_child_count(dev->of_node);
>>> + if (child_nodes > AHCI_MAX_PORTS) {
>>> + rc = -EINVAL;
>>> + goto err_out;
>>> + }
>>>
>>> /*
>>> * If no sub-node was found, we still need to set nports to
>>> * one in order to be able to use the
>>> * ahci_platform_[en|dis]able_[phys|regulators] functions.
>>> */
>>> - if (!child_nodes)
>>> - hpriv->nports = 1;
>>> + hpriv->nports = child_nodes ?: 1;
>>
>
>> This change is not necessary and makes the code far less easy to read.
>
> elaborate please. What change? What part of this change makes the code
> less easy to read?

You changed:

if (!child_nodes)
hpriv->nports = 1;

to:

hpriv->nports = child_nodes ?: 1;

That is the same. So the change is not needed in the first place, and worse,
makes the code way harder to read for no good reason.

>
> -Sergey
>
>>
>>>
>>> hpriv->phys = devm_kcalloc(dev, hpriv->nports, sizeof(*hpriv->phys), GFP_KERNEL);
>>> if (!hpriv->phys) {
>>
>>
>> --
>> Damien Le Moal
>> Western Digital Research

--
Damien Le Moal
Western Digital Research