Received-SPF: softfail (google.com: domain of transitioning linux-kernel-owner@vger.kernel.org does not designate 23.128.96.19 as permitted sender) client-ip=23.128.96.19;
From:   Ondrej Zary <linux@zary.sk>
To:     Sergey Shtylyov <s.shtylyov@omp.ru>
Subject: Re: [PATCH] pata_parport: add driver (PARIDE replacement)
Date:   Wed, 16 Mar 2022 12:28:05 +0100
User-Agent: KMail/1.9.10
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> <202203132219.59100.linux@zary.sk> <68e572f6-e1b6-8d04-900d-8621f607f3bc@omp.ru>
In-Reply-To: <68e572f6-e1b6-8d04-900d-8621f607f3bc@omp.ru>
MIME-Version: 1.0
Content-Type: Text/Plain;
  charset="utf-8"
Content-Transfer-Encoding: 7bit
Content-Disposition: inline
Message-Id: <202203161228.05700.linux@zary.sk>
Precedence: bulk

On Wednesday 16 March 2022, Sergey Shtylyov wrote:
> 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

OK, I was probably confused by ata_sff_check_status which uses ioread directly.

> [...]
> >>> 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()...

swab16 swaps always but pi_swab16 does not on big-endian. It's probably a bug but doing the correct thing by accident. Other protocol drivers completely ignore endianness, probably because PARIDE was meant for x86 only.

> [...]
> 
> MBR, Sergey
> 


-- 
Ondrej Zary