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Subject: Re: [PATCH] pata_parport: add driver (PARIDE replacement)
To:     Ondrej Zary <linux@zary.sk>
CC:     Damien Le Moal <damien.lemoal@opensource.wdc.com>,
        Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>,
        Tim Waugh <tim@cyberelk.net>, <linux-block@vger.kernel.org>,
        <linux-parport@lists.infradead.org>, <linux-ide@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>
References: <20220312144415.20010-1-linux@zary.sk>
 <a8189d8e-03e2-1b6f-3251-8e44e4e5e423@omp.ru>
 <202203132219.59100.linux@zary.sk>
From:   Sergey Shtylyov <s.shtylyov@omp.ru>
Organization: Open Mobile Platform
Message-ID: <68e572f6-e1b6-8d04-900d-8621f607f3bc@omp.ru>
Date:   Wed, 16 Mar 2022 11:50:44 +0300
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Hello!

On 3/14/22 12:19 AM, Ondrej Zary wrote:

[...]
>>> The pata_parport is a libata-based replacement of the old PARIDE
>>> subsystem - driver for parallel port IDE devices.
>>> It uses the original paride low-level protocol drivers but does not
>>> need the high-level drivers (pd, pcd, pf, pt, pg). The IDE devices
>>> behind parallel port adapters are handled by the ATA layer.
>>>
>>> This will allow paride and its high-level drivers to be removed.
>>>
>>> paride and pata_parport are mutually exclusive because the compiled
>>> protocol drivers are incompatible.
>>>
>>> Tested with Imation SuperDisk LS-120 and HP C4381A (both use EPAT
>>> chip).
>>>
>>> Note: EPP-32 mode is buggy in EPAT - and also in all other protocol
>>> drivers - they don't handle non-multiple-of-4 block transfers
>>> correctly. This causes problems with LS-120 drive.
>>> There is also another bug in EPAT: EPP modes don't work unless a 4-bit
>>> or 8-bit mode is used first (probably some initialization missing?).
>>> Once the device is initialized, EPP works until power cycle.
>>>
>>> So after device power on, you have to:
>>> echo "parport0 epat 0" >/sys/bus/pata_parport/new_device
>>> echo pata_parport.0 >/sys/bus/pata_parport/delete_device
>>> echo "parport0 epat 4" >/sys/bus/pata_parport/new_device
>>> (autoprobe will initialize correctly as it tries the slowest modes
>>> first but you'll get the broken EPP-32 mode)
>>>
>>> Signed-off-by: Ondrej Zary <linux@zary.sk>
>> [...]
>>> diff --git a/Documentation/admin-guide/blockdev/paride.rst b/Documentation/admin-guide/blockdev/paride.rst
>>> index e1ce90af602a..e431a1ef41eb 100644
>>> --- a/Documentation/admin-guide/blockdev/paride.rst
>>> +++ b/Documentation/admin-guide/blockdev/paride.rst
>> [...]
>>> diff --git a/drivers/ata/pata_parport.c b/drivers/ata/pata_parport.c
>>> new file mode 100644
>>> index 000000000000..783764626a27
>>> --- /dev/null
>>> +++ b/drivers/ata/pata_parport.c
>>> @@ -0,0 +1,819 @@
>> [...]
>>> +static void pata_parport_lost_interrupt(struct ata_port *ap)
>>> +{
>>> +	u8 status;
>>> +	struct ata_queued_cmd *qc;
>>> +
>>> +	/* Only one outstanding command per SFF channel */
>>> +	qc = ata_qc_from_tag(ap, ap->link.active_tag);
>>> +	/* We cannot lose an interrupt on a non-existent or polled command */
>>> +	if (!qc || qc->tf.flags & ATA_TFLAG_POLLING)
>>> +		return;
>>> +	/*
>>> +	 * See if the controller thinks it is still busy - if so the command
>>> +	 * isn't a lost IRQ but is still in progress
>>> +	 */
>>> +	status = pata_parport_check_altstatus(ap);
>>> +	if (status & ATA_BUSY)
>>> +		return;
>>> +
>>> +	/*
>>> +	 * There was a command running, we are no longer busy and we have
>>> +	 * no interrupt.
>>> +	 */
>>> +	ata_port_warn(ap, "lost interrupt (Status 0x%x)\n", status);
>>> +	/* Run the host interrupt logic as if the interrupt had not been lost */
>>> +	ata_sff_port_intr(ap, qc);
>>> +}
>>
>>    As I said, ata_sff_lost_interrupt() could be used instead...
> 
> It couldn't be used because it calls ata_sff_altstatus().

   And? That one used to call the sff_check_altstatus() method (which you define)
even before my patch:

https://git.kernel.org/pub/scm/linux/kernel/git/dlemoal/libata.git/commit/?h=for-next&id=03c0e84f9c1e166d57d06b04497e11205f48e9a8

[...]
>>> diff --git a/include/linux/pata_parport.h b/include/linux/pata_parport.h
>>> new file mode 100644
>>> index 000000000000..f1ba57bb319c
>>> --- /dev/null
>>> +++ b/include/linux/pata_parport.h
>>> @@ -0,0 +1,108 @@
[...]
>>> +static inline u16 pi_swab16(char *b, int k)
>>> +{
>>> +	union { u16 u; char t[2]; } r;
>>> +
>>> +	r.t[0] = b[2 * k + 1]; r.t[1] = b[2 * k];
>>> +	return r.u;
>>> +}
>>> +
>>> +static inline u32 pi_swab32(char *b, int k)
>>> +{
>>> +	union { u32 u; char f[4]; } r;
>>> +
>>> +	r.f[0] = b[4 * k + 1]; r.f[1] = b[4 * k];
>>> +	r.f[2] = b[4 * k + 3]; r.f[3] = b[4 * k + 2];
>>> +	return r.u;
>>
>>    Hey, I was serious about swab{16|32}p()! Please don't use home grown byte
>> swapping...
> 
> This crap comes from old paride.h and we can't get rid of it without touching the protocol drivers

   I don't argue about the *inline*s themselves, just about the ineffective code inside them.

> (comm.c and kbic.c). Maybe use something like:
> 
> #define pi_swab16(char *b, int k) 	swab16p((u16 *)&b[2 * k])

> but I'm not sure it's equivalent on a big-endian machine.

   These functions are endian-agnostic -- they swap always.
   If you only need to swab the bytes on big-endian machines, you should use cpu_to_le*() and/or
le*_to_cpu()...

[...]

MBR, Sergey