From: Mark Brown <broonie@kernel.org> To: Eddie James <eajames@linux.ibm.com> Cc: Vincent Whitchurch <vincent.whitchurch@axis.com>, krzysztof.kozlowski@linaro.org, andi@etezian.org, kernel@axis.com, alim.akhtar@samsung.com, linux-spi@vger.kernel.org, linux-kernel@vger.kernel.org, linux-samsung-soc@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v2 3/4] spi: Split transfers larger than max size Date: Fri, 23 Jun 2023 18:16:29 +0100 [thread overview] Message-ID: <ZJXTbb7zb9Q9T3QQ@finisterre.sirena.org.uk> (raw) In-Reply-To: <9cc6addc-cd41-7794-79a0-5c776946f492@linux.ibm.com> [-- Attachment #1: Type: text/plain, Size: 2907 bytes --] On Fri, Jun 23, 2023 at 11:45:19AM -0500, Eddie James wrote: > On 6/22/23 16:16, Mark Brown wrote: > > On Thu, Jun 22, 2023 at 02:48:36PM -0500, Eddie James wrote: > > > On 9/27/22 06:21, Vincent Whitchurch wrote: > > > > A couple of drivers call spi_split_transfers_maxsize() from their > > > > ->prepare_message() callbacks to split transfers which are too big for > > > > them to handle. Add support in the core to do this based on > > > > ->max_transfer_size() to avoid code duplication. > > > I've been testing AT25 functionality in linux 6.1 and I believe this patch > > > is breaking the AT25 protocol. It will split a write command up such that > > > some of the data is in a different transfer than the write enable and > > Could you be more specific about the manner in which you think this is > > breaking things? The size of transfer is immaterial to the client > Ok, I understand better now. Agreed it shouldn't make a difference, but this > is actually a limitation of the spi controller I'm using (spi-fsi). The > controller cannot handle multiple transfers keeping the chip select > enabled... I guess the driver can batch transfers in the message to get > around this, unless you want to add a flag for that behavior. Client drivers should in general just generate messages corresponding to the desired result visible to the device and let the controller worry about how to actually accomplish that, splitting transfers needlessly is just going to create overheads. If there's scatter/gather going on that does complicate things a bit though so it's not always going to happen. If the controller driver needs to rewrite the message to combine transfers then it should do that (or tell the core to do so on it's behalf), just like with splitting transfers due to length limits. > > In any case this is all based on the maximum transfer size advertised by > > the conteroller driver, if the device can physically handle larger > > transfers then there's no reason for it to set a limit. If the driver > > can't physically handle larger transfers and it does make a difference > > then the system simply won't work. > Yep, this is also an artifact of the spi-fsi driver having different > transfer size limits for writes and reads. Funnily enough the at25 driver > doesn't truly respect the max transfer size (it doesn't include the write > command and address bytes in the calculation against the max transfer size) > so that's how this worked previously. Yes, the logic there looks incorrect. As well as the issue you've identified the driver should really be using spi_max_message_size(), with a controller that can't control chip select effectivley like the FSI driver that'll be the same a the transfer size but other drivers will be able to chain multiple transfers together even if there's limits on the transfer length. [-- Attachment #2: signature.asc --] [-- Type: application/pgp-signature, Size: 488 bytes --]
WARNING: multiple messages have this Message-ID (diff)
From: Mark Brown <broonie@kernel.org> To: Eddie James <eajames@linux.ibm.com> Cc: Vincent Whitchurch <vincent.whitchurch@axis.com>, krzysztof.kozlowski@linaro.org, andi@etezian.org, kernel@axis.com, alim.akhtar@samsung.com, linux-spi@vger.kernel.org, linux-kernel@vger.kernel.org, linux-samsung-soc@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v2 3/4] spi: Split transfers larger than max size Date: Fri, 23 Jun 2023 18:16:29 +0100 [thread overview] Message-ID: <ZJXTbb7zb9Q9T3QQ@finisterre.sirena.org.uk> (raw) In-Reply-To: <9cc6addc-cd41-7794-79a0-5c776946f492@linux.ibm.com> [-- Attachment #1.1: Type: text/plain, Size: 2907 bytes --] On Fri, Jun 23, 2023 at 11:45:19AM -0500, Eddie James wrote: > On 6/22/23 16:16, Mark Brown wrote: > > On Thu, Jun 22, 2023 at 02:48:36PM -0500, Eddie James wrote: > > > On 9/27/22 06:21, Vincent Whitchurch wrote: > > > > A couple of drivers call spi_split_transfers_maxsize() from their > > > > ->prepare_message() callbacks to split transfers which are too big for > > > > them to handle. Add support in the core to do this based on > > > > ->max_transfer_size() to avoid code duplication. > > > I've been testing AT25 functionality in linux 6.1 and I believe this patch > > > is breaking the AT25 protocol. It will split a write command up such that > > > some of the data is in a different transfer than the write enable and > > Could you be more specific about the manner in which you think this is > > breaking things? The size of transfer is immaterial to the client > Ok, I understand better now. Agreed it shouldn't make a difference, but this > is actually a limitation of the spi controller I'm using (spi-fsi). The > controller cannot handle multiple transfers keeping the chip select > enabled... I guess the driver can batch transfers in the message to get > around this, unless you want to add a flag for that behavior. Client drivers should in general just generate messages corresponding to the desired result visible to the device and let the controller worry about how to actually accomplish that, splitting transfers needlessly is just going to create overheads. If there's scatter/gather going on that does complicate things a bit though so it's not always going to happen. If the controller driver needs to rewrite the message to combine transfers then it should do that (or tell the core to do so on it's behalf), just like with splitting transfers due to length limits. > > In any case this is all based on the maximum transfer size advertised by > > the conteroller driver, if the device can physically handle larger > > transfers then there's no reason for it to set a limit. If the driver > > can't physically handle larger transfers and it does make a difference > > then the system simply won't work. > Yep, this is also an artifact of the spi-fsi driver having different > transfer size limits for writes and reads. Funnily enough the at25 driver > doesn't truly respect the max transfer size (it doesn't include the write > command and address bytes in the calculation against the max transfer size) > so that's how this worked previously. Yes, the logic there looks incorrect. As well as the issue you've identified the driver should really be using spi_max_message_size(), with a controller that can't control chip select effectivley like the FSI driver that'll be the same a the transfer size but other drivers will be able to chain multiple transfers together even if there's limits on the transfer length. [-- Attachment #1.2: signature.asc --] [-- Type: application/pgp-signature, Size: 488 bytes --] [-- Attachment #2: Type: text/plain, Size: 176 bytes --] _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2023-06-23 17:16 UTC|newest] Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-09-27 11:21 [PATCH v2 0/4] spi: Fix DMA bugs in (not only) spi-s3c64xx Vincent Whitchurch 2022-09-27 11:21 ` Vincent Whitchurch 2022-09-27 11:21 ` [PATCH v2 1/4] spi: Save current RX and TX DMA devices Vincent Whitchurch 2022-09-27 11:21 ` Vincent Whitchurch 2022-09-27 11:21 ` [PATCH v2 2/4] spi: Fix cache corruption due to DMA/PIO overlap Vincent Whitchurch 2022-09-27 11:21 ` Vincent Whitchurch 2022-09-30 11:20 ` Marek Szyprowski 2022-09-30 11:20 ` Marek Szyprowski 2022-09-30 12:10 ` Robin Murphy 2022-09-30 12:10 ` Robin Murphy 2022-10-03 11:29 ` Vincent Whitchurch 2022-10-03 11:29 ` Vincent Whitchurch 2022-09-27 11:21 ` [PATCH v2 3/4] spi: Split transfers larger than max size Vincent Whitchurch 2022-09-27 11:21 ` Vincent Whitchurch 2023-06-22 19:48 ` Eddie James 2023-06-22 19:48 ` Eddie James 2023-06-22 21:16 ` Mark Brown 2023-06-22 21:16 ` Mark Brown 2023-06-23 16:45 ` Eddie James 2023-06-23 16:45 ` Eddie James 2023-06-23 17:16 ` Mark Brown [this message] 2023-06-23 17:16 ` Mark Brown 2022-09-27 11:21 ` [PATCH v2 4/4] spi: s3c64xx: Fix large transfers with DMA Vincent Whitchurch 2022-09-27 11:21 ` Vincent Whitchurch 2022-09-28 17:27 ` [PATCH v2 0/4] spi: Fix DMA bugs in (not only) spi-s3c64xx Mark Brown 2022-09-28 17:27 ` Mark Brown
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=ZJXTbb7zb9Q9T3QQ@finisterre.sirena.org.uk \ --to=broonie@kernel.org \ --cc=alim.akhtar@samsung.com \ --cc=andi@etezian.org \ --cc=eajames@linux.ibm.com \ --cc=kernel@axis.com \ --cc=krzysztof.kozlowski@linaro.org \ --cc=linux-arm-kernel@lists.infradead.org \ --cc=linux-kernel@vger.kernel.org \ --cc=linux-samsung-soc@vger.kernel.org \ --cc=linux-spi@vger.kernel.org \ --cc=vincent.whitchurch@axis.com \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is an external index of several public inboxes, see mirroring instructions on how to clone and mirror all data and code used by this external index.