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

[Damien Le Moal]

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@xxxxxxxxxxxxxxxxxxxx>
>>> Reviewed-by: Hannes Reinecke <hare@xxxxxxx>
>>>
>>> ---
>>>
>>> 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