From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5253C1BDA97; Fri, 6 Dec 2024 11:48:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1733485692; cv=none; b=nt63nswO4Fk70mh+U0Kj3dVwJ7uKKC7njAV6VkA5I7q/eAH/yyzWW67pD0dg53ZnY49Mz0pd/vMdVJC1ZdLRz/6K7AH3/sfok63noqlxwh/gJ5V2eUggUc+OsRkDeHgo8GVTLuAq3WV4n+dEhEL46eaFPBQpUt8n3UXMPJHcjJg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1733485692; c=relaxed/simple; bh=qEiT145v+mmmXz/X9So4yw/RdnpSM6fmg8D+g80PLnA=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=M+plK4sZ8l6kDoLGFzs0hA5r8CrsXnLFBmefso/RoFEy4Z7HEsZe7hij6uieeRVoaPYTHMd/tRAjaOufF9f9TGAg4UT2O9rgYZhE1oryUfgn0Pn/JH/MJlnaKh4u3CsUecgIkV5nSywvvxrybx94peYBda3CTbKaot0LyGTdSd8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=EOAAfRfF; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="EOAAfRfF" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A6A25C4CED1; Fri, 6 Dec 2024 11:48:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1733485691; bh=qEiT145v+mmmXz/X9So4yw/RdnpSM6fmg8D+g80PLnA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=EOAAfRfFmhScD8M4YKfBg2hzYH8fYRKO6PP8IZIL7Ra22OCa9M499fbQ+fQZ715Uu FvFVlvEe+fXm9svkgmCugWUW+noYen6B/6nWguggGORGE+7XAqjE1pNL1N3uKDzd5y n6G2Z1exSB00BxTvr1sardR1LSMTqkhupS1IMTBJyiNMoYszJ8E8fDp7Jbyxmr+zhI UYKFa6qjWlvv61+6eSrwexgt2y1Y7Ljs50KL8opS0XeRCvwTXn/SbMEUqF+kTlyaj+ ryKUFjVCrbYt524ZClofRwD/yxQmIxoyiqmdmGk+tuGzQuNdqdKa98fXWxB+YsATBW opKuZyDIwvP7g== Date: Fri, 6 Dec 2024 11:48:07 +0000 From: Conor Dooley To: Wolfram Sang Cc: linux-i2c@vger.kernel.org, Conor Dooley , Daire McNamara , Andi Shyti , Wolfram Sang , linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, valentina.fernandezalanis@microchip.com Subject: Re: [PATCH v1] i2c: microchip-core: actually use repeated sends Message-ID: <20241206-random-spectacle-9de88d412653@spud> References: <20240930-uneasy-dorsal-1acda9227b0d@spud> <20241001-haphazard-fineness-ac536ff4ae96@spud> <20241024-snagged-elated-d168d0d6bf35@spud> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="2o2i0BUpv0Ef1SLM" Content-Disposition: inline In-Reply-To: <20241024-snagged-elated-d168d0d6bf35@spud> --2o2i0BUpv0Ef1SLM Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Hey Wolfram, On Thu, Oct 24, 2024 at 10:36:33AM +0100, Conor Dooley wrote: > On Tue, Oct 01, 2024 at 11:16:24AM +0100, Conor Dooley wrote: > > On Tue, Oct 01, 2024 at 10:50:56AM +0200, Wolfram Sang wrote: > > > > At present, where repeated sends are intended to be used, the > > > > i2c-microchip-core driver sends a stop followed by a start. Lots of= i2c > > >=20 > > > Oh, this is wrong. Was this just overlooked or was maybe older hardwa= re > > > not able to generated correct repeated-starts? > >=20 > > Overlooked, because the devices that had been used until recently didn't > > care about whether they got a repeated start or stop + start. The bare > > metal driver upon which the Linux one was originally based had a trivial > > time of supporting repeated starts because it only allows specific sorts > > of transfers. I kinda doubt you care, but the bare metal implementation > > is here: > > https://github.com/polarfire-soc/polarfire-soc-bare-metal-library/blob/= 614a67abb3023ba47ea6d1b8d7b9a9997353e007/src/platform/drivers/mss/mss_i2c/m= ss_i2c.c#L737 > >=20 > > It just must have been missed that the bare metal method was not replac= ed. > >=20 > > > > devices must not malfunction in the face of this behaviour, because= the > > > > driver has operated like this for years! Try to keep track of wheth= er or > > > > not a repeated send is required, and suppress sending a stop in the= se > > > > cases. > > >=20 > > > ? I don't get that argument. If the driver is expected to do a repeat= ed > > > start, it should do a repeated start. If it didn't, it was a bug and = you > > > were lucky that the targets could handle this. Because most controlle= rs > > > can do repeated starts correctly, we can also argue that this works f= or > > > most targets for years. In the unlikely event that a target fails aft= er > > > converting this driver to proper repeated starts, the target is buggy > > > and needs fixing. It would not work with the majority of other > > > controllers this way. > > >=20 > > > I didn't look at the code but reading "keeping track whether rep start > > > is required" looks wrong from a high level perspective. > >=20 > > I think if you had looked at the code, you'd (hopefully) understand what > > I meant w.r.t. tracking that. > > The design of this IP is pretty old, and intended for use with other > > logic implemented in FPGA fabric where each interrupt generated by > > the core would be the stimulus for the state machine controlling it to > > transition state. Cos of that, when controlling it from software, the > > interrupt handler assumes the role of that state machine. When I talk > > about tracking whether or not a repeated send is required, that's > > whether or not a particular message in a transfer requires it, not > > whether or not the target device requires them or not. > >=20 > > Currently the driver operates by iterating over a list of messages in a > > transfer, and calling send() for each one, and then effectively "loopin= g" > > in the interrupt handler until the message has been sent. By looking at > > the current code, you can see that the completion's "lifecycle" matches > > that. Currently, at the end of each message being sent > > static irqreturn_t mchp_corei2c_handle_isr(struct mchp_corei2c_dev *id= ev) > > { > > =09 > > > > =09 > > /* On the last byte to be transmitted, send STOP */ > > if (last_byte) > > mchp_corei2c_stop(idev); > > =09 > > if (last_byte || finished) > > complete(&idev->msg_complete); > > =09 > > return IRQ_HANDLED; > > } > > a stop is put on the bus, unless !last_byte, which is only true in error > > cases. Clearly I don't need to explain why that is a problem to you... > > You'd think that we could do something like moving the stop out of the > > interrupt handler, and to the loop in mchp_corei2c_xfer(), where we have > > access to the transfer's message list and can check if a stop should be > > sent or not - that's not really possible with the hardware we have. > >=20 > > When the interrupt handler completes, it clears the interrupt bit in the > > IP, as you might expect. The controller IP uses that as the trigger to > > transition state in its state machine, which is detailed in > > https://ww1.microchip.com/downloads/aemDocuments/documents/FPGA/Product= Documents/UserGuides/ip_cores/directcores/CoreI2C_HB.pdf > > On page 23, row 0x28, you can see the case that (IIRC) is the > > problematic one. It is impossible to leave this state without triggering > > some sort of action. > > The only way that I could see to make this work correctly was to get the > > driver track whether or not the next message required a repeated start = or > > not, so as to transition out of state 0x28 correctly. > >=20 > > Unfortunately, then the clearing of the interrupt bit causing state > > transitions kicked in again - after sending a repeated start, it will > > immediately attempt to act (see state 0x10 on page 23). Without > > reworking the driver to send entire transfers "in one go" (where the > > completion is that of the transfer rather than the message as it > > currently is) the controller will re-send the last target address + > > read/write command it sent, instead of the next one. That's why there's > > so many changes outside of the interrupt handler and so many additional > > members in the controller's private data structure. > >=20 > > I hope that that at least makes some sense.. > >=20 > > > The driver > > > should do repeated start when it should do repeated start. > >=20 > > Yup, that's what I'm trying to do here :) >=20 > I'd like to get this fix in, and Andi only had some minor comments that > didn't require a respin. I don't want to respin or resend while this > conversation remains unresolved. Could you please respond to this thread? I don't want to respin without resolving this conversation since I feel like we'd just end up having it all over again. Thanks, Conor. --2o2i0BUpv0Ef1SLM Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iHUEABYIAB0WIQRh246EGq/8RLhDjO14tDGHoIJi0gUCZ1LkdwAKCRB4tDGHoIJi 0m1XAQCdwXDfHtbOt/o2xFRN6ijk2Q9nmrqhXvVgFV7mO2qxswD7BTQa1bc4lUaZ wcUgcQzSvYG39FZbjfGmB8Hf2jCKPAM= =TYme -----END PGP SIGNATURE----- --2o2i0BUpv0Ef1SLM--