linux-kernel - Re: [PATCH 3/4] pata_parport: add custom version of wait_after

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Date:   Wed, 4 Oct 2023 08:44:39 +0900
From:   Damien Le Moal <dlemoal@...nel.org>
To:     Sergey Shtylyov <s.shtylyov@....ru>, Ondrej Zary <linux@...y.sk>,
        Sudip Mukherjee <sudipm.mukherjee@...il.com>
Cc:     Christoph Hellwig <hch@....de>, Tim Waugh <tim@...erelk.net>,
        linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] pata_parport: add custom version of wait_after_reset

On 10/4/23 01:55, Sergey Shtylyov wrote:
> On 10/3/23 3:55 AM, Damien Le Moal wrote:
> 
> [...]
>>> Some parallel adapters (e.g. EXP Computer MC-1285B EPP Cable) return
>>> bogus values when there's no master device present. This can cause
>>> reset to fail, preventing the lone slave device (such as EXP Computer
>>> CD-865) from working.
>>>
>>> Add custom version of wait_after_reset that ignores master failure when
>>> a slave device is present. The custom version is also needed because
>>> the generic ata_sff_wait_after_reset uses direct port I/O for slave
>>> device detection.
>>>
>>> Signed-off-by: Ondrej Zary <linux@...y.sk>
>>> ---
>>>  drivers/ata/pata_parport/pata_parport.c | 65 ++++++++++++++++++++++++-
>>>  1 file changed, 64 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/ata/pata_parport/pata_parport.c b/drivers/ata/pata_parport/pata_parport.c
>>> index cf87bbb52f1f..b3db953e615a 100644
>>> --- a/drivers/ata/pata_parport/pata_parport.c
>>> +++ b/drivers/ata/pata_parport/pata_parport.c
>>> @@ -80,6 +80,69 @@ static bool pata_parport_devchk(struct ata_port *ap, unsigned int device)
>>>  	return (nsect == 0x55) && (lbal == 0xaa);
>>>  }
>>>  
>>> +static int pata_parport_wait_after_reset(struct ata_link *link,
>>> +					 unsigned int devmask,
>>> +					 unsigned long deadline)
>>> +{
>>> +	struct ata_port *ap = link->ap;
>>> +	struct pi_adapter *pi = ap->host->private_data;
>>> +	unsigned int dev0 = devmask & (1 << 0);
>>> +	unsigned int dev1 = devmask & (1 << 1);
>>> +	int rc, ret = 0;
>>> +
>>> +	ata_msleep(ap, ATA_WAIT_AFTER_RESET);
>>> +
>>> +	/* always check readiness of the master device */
>>> +	rc = ata_sff_wait_ready(link, deadline);
>>> +	/* some adapters return bogus values if master device is not present,
>>> +	 * so don't abort now if a slave device is present
>>> +	 */
>>
>> In addition to Sergey's comment, please move this comment inside the "if", or
>> even better, merge it with the otherwise not very useful "always check
>> readiness..." comment.
> 
>    That comment was copied from ata_sff_wait_after_reset(), I think...

Even if that is the case. let's not copy bad stuff as is but rather improve it.


-- 
Damien Le Moal
Western Digital Research