From mboxrd@z Thu Jan 1 00:00:00 1970 From: sudeep.holla@arm.com (Sudeep Holla) Date: Thu, 2 Nov 2017 10:47:46 +0000 Subject: [PATCH] mailbox: add support for doorbell/signal mode controllers In-Reply-To: References: <1509553964-4451-1-git-send-email-sudeep.holla@arm.com> <59a05fcb-ff30-0683-144e-93521a7413f9@arm.com> Message-ID: <4268c9d9-dc1e-0bd7-3fac-790c2d42b54b@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 02/11/17 02:39, Jassi Brar wrote: > On Wed, Nov 1, 2017 at 11:45 PM, Sudeep Holla wrote: >> >> >> On 01/11/17 18:03, Jassi Brar wrote: >>> On Wed, Nov 1, 2017 at 10:02 PM, Sudeep Holla wrote: >>> >>>> >>>> Such controllers don't need to transmit any data, they just transmit >>>> the signal. In such controllers the data pointer passed to >>>> mbox_send_message is passed to client via it's tx_prepare callback. >>>> Controller doesn't need any data to be passed from the client. >>>> >>> Some controllers need a non-zero value written to a register in order >>> to trigger the signal. >> >> You are right, just right non-zero or whatever controller value to >> trigger the interrupt to remote. >> >>> That register is visible to the remote. While the data/packet is setup >>> during tx_prepare() callback. >> >> Agreed. >> >>> You are overlooking this class of doorbell controllers. >>> >> >> Not sure what do you mean by that ? >> > Such doorbell controllers can't use send_signal(chan) because they > need that non-zero value from client to send over the shared register. > You are assuming every protocol implements just one command. > No that non-zero value is not client specific, it's entirely controller specific. Not sure why do you think I am assuming every protocol implements just one command. >>>> >>>> This is rough idea I have on extending mailbox interface to support >>>> the doorbell requirements. >>>> >>> What doorbell requirements does the api not support? >>> QComm's APCS IPC is what you call a "doorbell" controller and is >>> already supported by the API. After looking at this, you will see that doorbell has not data specific to client in the above case. unsigned long idx = (unsigned long)chan->con_priv; writel(BIT(idx), apcs->reg); So it's channel specific, same in mailbox-sti >> Again agreed. But see below for reason to create this API. >> >>>> The new API send_signal will eliminate the >>>> issue Jassi has explained in earlier discussion with respect to generic >>>> message format using Rockchip example. >>>> >>> Sorry I don't see how. >>> Please explain how can send_signal() api be used by, say, rockchip to >>> support SCMI? >>> >> >> 80 writel_relaxed(msg->cmd, mb->mbox_base + >> MAILBOX_A2B_CMD(chans->idx)); >> 81 writel_relaxed(msg->rx_size, mb->mbox_base + >> >> 82 MAILBOX_A2B_DAT(chans->idx)); >> >> 83 >> >> will be replaced with >> >> writel(whatever_value_to trigger_signal, MAILBOX_A2B_CMD(chans->idx)); >> >> in its send_signal function. >> > 1) Where does the "whatever_value_to_trigger_signal" come from? Controller specific. > That has to come from client. No. > You can not dictate the channel transfers a fixed u32 value over its >lifetime. SCMI may use one command code but other protocols use more. Yes if it's just a doorbell, see the above 2 cases I have pointed out. > > 2) Using 'rx_size' is not a software choice made in the driver. The > _hardware_ has two registers shared with remote side - a CMD and a > DATA register. So the driver (written agnostic to any particular > client) would naturally expect the command+data from the client to be > programmed in to CMD and DAT registers. > OK, if this controller needs to be used in doorbell mode for SCMI, we can send one fixed cmd and fixed rx_size() or 1 based on inclusive or exclusive). > >>> I am not convinced we should clone an api just so that a client driver >>> becomes simpler. Esp when it shifts, and not avoid, the additional >>> code (to support the client) onto the provider side. >>> >> >> It doesn't tie the data format with particular mailbox controller. >> send_data has void *data and the interpretation is controller specific. >> send_signal on the other handle can implemented by the controllers which >> knows how and can trigger the specific signal to the remote. >> > Yeah that's what I said - you want to make a client simpler by pushing > the code requirement onto the provider side. > No, I want to support generic case of mailbox doorbell instead of creating another unnecessary abstraction layer > For example, you mean we modify the provider rockchip-mailbox.c by implementing > > rockchip_send_signal(chan) > { > struct rockchip_mbox_msg msg; > > msg.cmd = chan->idx; //only one command supported by the channel !!! Yes, it's just a doorbell. That actual data is transmitted or shared elsewhere. This doorbell is a signal to the remote to examine that, > msg.rx_size = 0; > > rockchip_send_data(chan, (void*) &msg); > } > > whereas I suggest this SCMI specific code should be part of > transport/mapping shim layer of SCMI. > Yes that's what I did with abstraction and few think including me that it's unnecessary abstraction for such a generic use. -- Regards, Sudeep